API changes to allow for more mounting styles

NODE NAMES:

The base name of a node can be whatever you want.  The basic wall sign
will keep the node name you give, while its hanging, on-pole, and yard
variants will, where applicable, use the same name, with "_onpole",
"_hanging", or "_yard" appended.

One exception:

If your node has "_wall" in its name, that bit will be stripped-out when
generating the above node variations.  For example:

"default:sign_wall_wood"

...will become...

"default:sign_wood_onpole"
"default:sign_wood_hanging"
"default:sign_wood_yard"

MODELS:

The base sign model and entity files must now be named:

sign:   mymod_foosign_wall.obj
        mymod_foosign_facedir_wall.obj

entity: mymod_foosign_entity_wall.obj

their other variants, where applicable, must be:

mymod_foosign_onpole.obj
mymod_foosign_hanging.obj
mymod_foosign_yard.obj

mymod_foosign_entity_onpole.obj
mymod_foosign_entity_hanging.obj
mymod_foosign_entity_yard.obj

For `facedir` signs, the "_facedir" in the base sign model filename is
automatically stripped from the name when generating the entity model
filename, as entities don't have a concept of wallmounted/facedir/etc.
For example:

"mymod_foosign_facedir_wall.obj"

...will become...

"mymod_foosign_entity_wall.obj"

* allow passing custom onpole, hanging, and yard sign models, for
situations where the filename(s) thereof can't be derived from the base
sign model filename.

* allow passing a custom pole mount, hanging, and yard sign stick
textures as the third, fourth, and fifth tiles{} entries, respectively
(independent of the above model file option)

* fine-tuned the pole mount on the standard sign models to eliminate
overlapping faces (so it looks better with basic_signs' glass sign.

* Move basic_signs wooden yard sign back to signs_lib.

API.md

@@ -16,6 +16,17 @@ In this text, common terms such as `pos`, `node`, or `placer`/`digger` will not
 
     Default: `"mesh"`
 
+  * `tiles = {table}`
+
+    Since this is a sign-specific library, this parameter behaves rather different from what you would normally use in `minetest.register_node()`.  The first two entries are mandatory.  The third, fourth and fifth entries are optional, depending on which mounting styles are enabled for a given node.
+
+    * entry 1: the front and back of the sign.
+    * entry 2: the sides/edges
+    * entry 3: texture for the pole mount.  If unspecified, the standard pole mount image is used, if needed.
+    * entry 4: texture for the hanging part.  If unspecified, the standard hanging chains image is used, if needed.
+    * entry 5: texture for the yard sign stick.  If unspecified, "default_wood.png" is used, if needed.
+    * entry 6: ignored.
+
   * `mesh = "string"`
 
     Default: `"signs_lib_standard_wall_sign.obj"`.
@@ -34,6 +45,11 @@ In this text, common terms such as `pos`, `node`, or `placer`/`digger` will not
 
     Default: whatever the `inventory_image` is set to (if anything).
 
+  * `selection_box = {table}`
+
+    Works the same as usual.  A helper function exists to create boxes by specifying only and X/Y size and offset:
+    `signs_lib.make_selection_boxes()` (see below).
+
   * `groups = {table}`
 
     Sets the sign's groups, as usual.  In addition to whatever arbitrary groups you may have in mind, there are two presets available (both of which have `attached_node` removed, and `sign = 1` added):
@@ -92,6 +108,23 @@ In this text, common terms such as `pos`, `node`, or `placer`/`digger` will not
 
     Default: `signs_lib.update_sign`
 
+  * `onpole_mesh = "string"`
+  * `hanging_mesh = "string"`
+  * `yard_mesh = "string"`
+
+    If your node needs a custom model for its on-pole, hanging, and/or yard variants, specify them here, as needed.  The materials and textures behave the same on these as on other sign models.  All sign model filenames are still derived from the base sign model, when not overridden here (so these can be totally arbitrary filenames).
+
+    Default: the normal "_onpole", "_hanging", or "_yard" version of the model specified by `mesh`.
+
+  * `onpole_selection_box = {table}`
+  * `hanging_selection_box = {table}`
+  * `yard_selection_box = {table}`
+  * `onpole_node_box = {table}`
+  * `hanging_node_box = {table}`
+  * `yard_node_box = {table}`
+
+    If your node needs special handling for its onpole-, hanging-, or yard-mode selection boxes or for their collision info (which `signs_lib` always uses the node's `node_box` item for), you can specify them here.  Same syntax as the regular `selection_box` setting.
+
   * `default_color = "string"`
 
     Sets the default text color for this sign, in hexadecimal (`0-9`, `a-f`), from the standard Linux/IRC/CGA color palette.  Same as the colors shown in the sign's formspec.
@@ -165,22 +198,26 @@ In this text, common terms such as `pos`, `node`, or `placer`/`digger` will not
 
   * `allow_hanging = bool`
 
-    If `true`, allow the registration function to create a "hanging from the ceiling" version of the initial, base sign node.
+    If `true`, allow the registration function to create a "hanging from the ceiling" version of the initial, base sign node.  Its name will be the same as the base node name, with "_wall" deleted from the name (if present), and "_hanging" appended.  For example, "default:sign_wall_wood" becomes "default:sign_wood_hanging".
 
     Default: `nil`
 
   * `allow_onpole = bool`
 
-    Allow creation of an on-pole variant of the base sign.
+    Allow creation of an on-pole variant of the base sign, named the same as the base sign, with "_wall" deleted and "_onpole" appended.  Example: "default:sign_wall_wood" becomes "default:sign_wood_onpole"
 
     Default: `nil`
 
   * `allow_onpole_horizontal = bool`
 
-    Allow creation of an on-horizontal-pole variant.  This flag is independent of `allow_onpole`; the mod may specify either or both.
+    Allow creation of an on-horizontal-pole variant.  This flag is independent of `allow_onpole`; the mod may specify either or both.  Its name will be the base node name, with "_wall" deleted and "_onpole_horiz" appended.  Example:  "default:sign_wall_wood" becomes "default:sign_wood_onpole_horiz".
 
     Default: `nil`
 
+  * `allow_yard = bool`
+
+    Allow creation of a yard sign variant, named the same as the base sign, with "_wall" deleted and "_yard" appended.  Example: "default:sign_wall_wood" becomes "default:sign_wood_yard"
+
   * `allow_widefont = bool`
 
     Just what it says on the tin.  If enabled, the formspec will have a little "on/off switch" left of the "Write" button, to select the font width.