Ability to select Minetest API version

[S-S-X]

Add Minetest version parameter to configuration and when set use version specific Minetest core libraries.

Requires some easy way to track and update Minetest core libraries, possibly some script to fetch files from commit tagged by version.
Should probably still keep copies in mineunit repository and do updates to new version manually: execute script, resolve possible problems like moved/renamed libraries, commit new version libraries to mineunit repository.

Simplest would probably be putting libraries to subdirectories named after Minetest version.
Default Minetest version should probably be just static value in default configuration.

Related:

• Refactoring Mineunit configuration system #88

[S-S-X]

Finding deprecated and added core API methods (C++ exports only, not Lua side of core API): https://discord.com/channels/369122544273588224/749727888659447960/889649776377864252

https://github.com/minetest/minetest/blob/2628316842e9c3fc1c54c6d57505c7851fa83490/src/script/lua_api/l_object.cpp#L2336-L2338

Checkout tagged versions and grep luamethod* stuff from there, ones registered with luamethod_aliased are probably in deprecation process.
Others can be fairly easily wired into Mineunit classes, for most part naming already follows Minetest C++ class naming. Some things should be renamed or aliased here, for example Mineunit Player.

Some things are simple and can be wired to Mineunit classes directly while other things require bit more complex parsing, for example https://github.com/minetest/minetest/blob/2628316842e9c3fc1c54c6d57505c7851fa83490/src/script/lua_api/l_playermeta.cpp#L108-L122

[S-S-X]

Partially implemented in #74 but only for engine Lua libraries, rest of it has to be implemented somehow.
Possibly through base implementation with loadable version specific extensions to allows introducing and deprecating methods.

For example Player definition would be split like this:

• player.lua Base for Player, Mineunit internal stuff, very basic implementation, common helper functions
  • engine
    • 5.2.0
      • player.lua Stuff added for 5.2.0 and overriding deprecated things
    • 5.5.0
      • player.lua Stuff added for 5.5.0 and overriding deprecated things

Main definition introduces Player as globally available class, version specific stuff could be better if returning extension that can be merged into base.
This allows for example easily reusing code from engine/5.2.0/player.lua in engine/5.5.0/player.lua extension without duplicating implementation.

Similar should work fine for all current classes and function libraries.