This is a (first attempt at) adding flavor support to USES=lua, plus some additional options.
The intent is to allow the following:
- Lua modules like devel/lua-stdlib-* can be changed to use flavors to keep their dependencies straight, and some helper definitions in lua.mk make it easier for them to keep their documentation subdirs separate
- The lang/lua ports themselves could be changed to use USES=lua:envcore,NN to centralize the definitions of all the LUA_* variables in one place, rather than duplicating them between lua.mk and lang/luaNN/Makefile
- Applications that use Lua probably wouldn't want to use the flavors option, but can now use LUA_FLAVOR when declaring dependencies on libs
- More version range options are supported, e.g. USES=lua:52-54 or USES=lua:-53
A functional change is that this version makes no attempt to look at what versions of Lua are already installed - that seems to me to be a very bad idea.