Matrix stack system should be reviewed but, in the meantime,
currentMatrix should be reseted in order of 3d to work

If not using busy wait loop, linkage with WINMM in Windows platform is
required

Note that this solution is a temporal patch, not properly tested and
prone to fail, specially if matrix are pushed into the stack...

- Added: ImageAlphaClear()
- Added: ImageAlphaPremultiply()
- Reorganized some functions

- Renamed enum TextureFormat to PixelFormat for consistency
- Added support for pixel format UNCOMPRESSED_R32
- Using GetPixelDataSize() where required

Just found I need that function...

Using default font texture as base white texture for rectangles reduces
draw calls considerably, actually, raygui can be drawn with a single
pass!

Issues when dealing with FBOs

Review comments

Functionality integrated in DrawRectangle() and selectable with config
flag USE_DEFAULT_FONT_TEXTURE

Support external GLFW usage
Renamed some flags for consistency

I think is clearer this way...

Trace log messages could be configured with this function to select wich
ones are shown

That function depends on SavePNG() and forces platform check on textures
module, that behaviour should be changed, platform definition should be
only required on core module...

OpenAL audio backend is being forced on HTML5 and OSX

Audio module requires a complete formatting review....

Monotonic time since InitWindow() could be retrieved with this function.

Reviewing GetTime() functionality

Some programs like tools could not require audio support

If shader file could not be found on loading it crashed, instead added
fallback to default shader!

Let the user choose if using rres external library

Less maintenance overhead that way,
given that make/CMake now also do library versioning.