Executables that use libbullet are now 1 MiB smaller (stripped!).

This lets us get rid of m_autorelease and m_destroy and we’ll be able
to implement init_game/init_draw later, for stuff that must happen
on the render thread.

Controller::WasKeyReleasedThisFrame() is now keyboard->key_released() so
there is usually no need for a controller. They will completely disappear
when joystick axis binding has been ported to InputDevice.

In particular, get rid of the enum magic; we can use map<string,int> if we
really need some named enums. Which we usually don’t.

The scene now owns its renderer, so there is no need to keep a list
of existing renderers and to call Renderer::Get().

Let’s be honest, I’m never gonna use it in its current form.

We used to have lol::map::empty() to empty maps, but in std::map
this method is called clear(). It sounds safe to harmonise between
our types and have lol::array::clear() too.

debug draw fixes are really un-numerous in ze lol, it seems

getter default params are better now

Next pass is clean-up and fix of all the old usage

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.

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.

We already have the convenient degrees() and radians() functions to convert
between angle formats. This commit involves a lot of refactoring here and
there and I may have missed some places where conversions were needed. But
hopefully there aren’t may such places.