On move support aka jumpdrive compat (#9)

* whitespace and minetest. -> core.

- use same whitespace style throughout and fix some indents.
- change from minetest. to core. namespace.

* Update Readme: Minetest -> Luanti

* add luacheck

* update optional depends

* luacheck cleanups

- unused arguments
- shaddowed vars
- var redeclarations
- some whitespace involved in above lines

* clean close of file after reading

* avoid duplicate code

save some lines and some extra method calls.

* avoid error: "unknown global"

* stray whitespace fixups

* whitespace: switch all files to same indent character

tabs -> spaces

* refactor weird declaration

* whitespace: two stray spaces

...that slipped through the cracks on previous whitespace edit

* fix shaddowing global table

* reduce amount of times transformation string is calculated

* use ipairs feature

or use the faster repeat-until-loop

* cap max amount of layers

fixes #5

* fix #5 make transform history non-global

fixes #5
transformation history was shared by all users and kept growing as it
was never truely reset. Every time a user
used a banner a white background was dumped on top of the
stack making it possible to crash the server through an
overflow to core.serialize() function.

* minimize metadata size

also changed banners.max_transformations to
banners.max_undo_levels and lowered the value substantially.

* add versioning

* add recoverable per player history with saved colour

* rename update_all -> update_preview_inv

since it isn't updating everything, only
the preview and the inventory item

* dynamically update masks

to reflect the currently selected colour.

* banner always exists

even if only "" it exists and there isn't an error.
not adding "" or texture string, causes a non critical error.

* use same function declaration style throughout

* remove set_banner_texture()

only used once and is easy enough to have inline

* preserve player undo-history over joins

player could have timed-out and thus lost their history.
It isn't crucial to remove their history, so let's give
them this feature.

* refactor: reusable transformation string creation

unfortunately the git diff is a bit messy on this one.
Nothing changed with:
- banners.Banner
- banners.Banner:new
- banners.Banner:push_transform
- banners.Banner:pop_transform

content of banners.Banner:get_transform_string was moved
to banners.transform_table_to_string with very few changes

* add transform_string_to_table

allows us to add more features such as:
- clean existing banners to slim down data
- read transforms from items in inventory -> allow players
  to change existing patterns without having to start from
  scratch.

* cleanup old banners when their entities are generated

* read item meta allowing players to edit existing banners

* version bump

* oopsie fixes

* remove stray debug point

* add chatcommand banners_fix

fixes #7
provides a work-around for the engine problem with entities.

* sensitive github luacheck syntax

* version bump

* cleanup: compact node definitions

* adds [jumpdrive] compat

github.com/mt-mods/jumpdrive

closes https://github.com/mt-mods/jumpdrive/issues/90

* also make factions banners jump-able

just for completeness sake

chatcommands.lua

@@ -0,0 +1,53 @@
+-- Due to some engine troubles there are sometimes stray
+-- banner entities and more rarely there are banner nodes without entities.
+-- Calling this command fixes both situations.
+core.register_chatcommand("banners_fix", {
+    description = "recreates the banner-visuals in your area",
+    func = function(name)
+        local player = core.get_player_by_name(name)
+        if not player then
+            return
+        end
+
+        local pos = player:get_pos()
+        local t1 = core.get_us_time()
+
+        local radius = 10
+        local entity_count = 0
+        local objects = core.get_objects_inside_radius(pos, radius)
+        for _, v in ipairs(objects) do
+            local e = v:get_luaentity()
+            if e and e.name == "banners:banner_ent" then
+                entity_count = entity_count + 1
+                v:remove()
+            end
+        end
+
+        local pos1 = vector.subtract(pos, radius)
+        local pos2 = vector.add(pos, radius)
+        local nodes = {
+            "banners:wooden_banner",
+            "banners:steel_banner",
+        }
+        if core.get_modpath("factions") then
+            table.insert_all(nodes, {
+                "banners:power_banner",
+                "banners:death_banner",
+
+            })
+        end
+        local pos_list = core.find_nodes_in_area(pos1, pos2, nodes)
+
+        for _, node_pos in ipairs(pos_list) do
+            core.add_entity(node_pos, "banners:banner_ent")
+        end
+
+        local t2 = core.get_us_time()
+        local diff = t2 - t1
+        local millis = diff / 1000
+
+        return true, "Removed " .. entity_count .. " banner entities and restored "
+            .. #pos_list .. " banners in " .. millis .. " ms"
+    end
+})
+