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

Added next BSD OS

Removed GLFW3 and OpenAL Soft dependencies

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.

Update CONTRIBUTING.md

* `Alien::raylib` downloads raylib, builds it and installs it in the Perl module path (Basically abusing CPAN as package manager)
* `Graphics::Raylib::XS` depends on `Alien::raylib` and reexports all C symbols as XS symbols usable in Perl
* `Graphics::Raylib` depends on `Graphics::Raylib::XS` and is the actual Perl wrapper with a Perlish API, which users should be using

Contributors added to contributing file

Reviewing GetTime() functionality

Some programs like tools could not require audio support

Develop

Build shared libs, games and examples on CI

Now with external OpenAL and GLFW dependencies removed,
we don't have to worry about installing them in CI.
Shared libraries are now always built along with static libs.
Games and examples are built everwhere except for Visual Studio,
because Physac needs pthreads, which VS doesn't provide.