This will allow us to generate sounds on the fly on several dedicated
channels. Until now we could only play fully loaded samples.

Input was broken, as well as palette generation, and even texture
upload. Should be all good now.

We have no hope of extending lua_State to add more data to it, because
that object may be created by Lua itself, for instance within a coroutine,
and it has no knowledge of our version of the object.

This has proved unreliable because coroutines create whole new environments,
so one of the only ways to store user data and access it even from coroutines
is to use lua_setglobal().

This will help us deal with shader name collision. Breaks the Windows
build for the moment, unfortunately.

This allows actors to perform draw commands in TickDraw(), even
if it’s not exactly what we want in the future.

For now the flags are: --disable-doc --disable-test
--disable-samples --disable-tutorial.

All these changes will allow us to more easily add Lol Engine as a
submodule of another Git project.

Travis-CI is so out of date that if you want something as simple as
libsdl2-dev you need to enable sudo and use the huge VM environment
instead of the containers that boot in a few seconds.