Fix warnings regarding use_texture_alpha

Add use_texture_alpha = "clip" for standard signs.
Break Minetest 5.4< compatibility.

api.lua

@@ -252,7 +252,10 @@ function signs_lib.set_obj_text(pos, text)
 	local text_ansi = Utf8ToAnsi(text)
 	local n = minetest.registered_nodes[minetest.get_node(pos).name]
 	signs_lib.delete_objects(pos)
-	signs_lib.spawn_entity(pos, signs_lib.make_sign_texture(split(text_ansi), pos) )
+	-- only create sign entity for actual text
+	if text_ansi and text_ansi ~= "" then
+		signs_lib.spawn_entity(pos, signs_lib.make_sign_texture(split(text_ansi), pos) )
+	end
 end
 
 -- rotation

depends.txt

@@ -1,7 +0,0 @@
-default
-intllib?
-screwdriver?
-streetspoles?
-streetlamps?
-cottages?
-prefab_redo?

description.txt

@@ -1 +0,0 @@
-Adds signs with readable text.

mod.conf

@@ -1,2 +1,6 @@
 name = signs_lib
+author = VanessaE
+depends = default
+optional_depends = intllib, screwdriver, streetspoles, streetlamps, cottages, prefab_redo
+description = Adds signs with readable text.
 min_minetest_version = 5.2.0

standard_signs.lua

@@ -14,7 +14,8 @@ signs_lib.register_sign("default:sign_wall_wood", {
 	allow_widefont = true,
 	allow_onpole = true,
 	allow_onpole_horizontal = true,
-	allow_yard = true
+	allow_yard = true,
+	use_texture_alpha = "clip",
 })
 
 signs_lib.register_sign("default:sign_wall_steel", {
@@ -35,7 +36,8 @@ signs_lib.register_sign("default:sign_wall_steel", {
 	allow_widefont = true,
 	allow_onpole = true,
 	allow_onpole_horizontal = true,
-	allow_yard = true
+	allow_yard = true,
+	use_texture_alpha = "clip",
 })
 
 minetest.register_alias("signs:sign_hanging",                   "default:sign_wood_hanging")