This commit should bring the mini_al backend up to feature parity with
the OpenAL backend.

...to define proper values

Compiling GLFW library with raylib avoids external dependencies, this
way we solve version problems in some platforms

Now header is truly multiplatform...

Actually still a small pending check on XBOX gamepad controls that
hopefully will be removed with next GLFW 3.3

Store the default shaders

libEGL and libGLESv2 have been renamed on latest Raspbian Stretch
version (also included on latest Jessie upgrade).

It seems to be done to avoid conflicts between official Mesa libs and
Broadcomm provided ones.

USE_DEPTH_RENDERBUFFER on OpenGL 2.1

Not tested, could have errors

On RPI, after latest drivers update, models were not rendered properly
cause of that...

Have SetShaderValue(i) take a const pointer

Could correct possible issues on OpenGL 1.1

C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\bin>dumpbin.exe
D:\GitHub\raylib\release\libs\win32\msvc\raylib.dll /DEPENDENTS

Microsoft (R) COFF/PE Dumper Version 14.00.24215.1
Copyright (C) Microsoft Corporation.  All rights reserved.

Dump of file D:\GitHub\raylib\release\libs\win32\msvc\raylib.dll

File Type: DLL

Image has the following dependencies:

KERNEL32.dll
glfw3.dll
OpenAL32.dll

Summary

4000 .data
1000 .gfids
23000 .rdata
5000 .reloc
1000 .rsrc
68000 .text
1000 _RDATA

Added support for raylib DLL building on MSVC

- Review RPI compilation (core_drop_files not supported)
- Review ImageFormat(), some issues
- GetTextureData() reviewed for RPI

Corrected issue with RPI_CROSS_COMPILE

Added support FreeBSD

Improve second option to retrieve texture data from fbo...

Still requires some testing...

...while reviewing GetTextureData() functionality on OpenGL ES 2.0

Hopefully new videos comming soon...

- Added new function: GenImageColor()

ImageDraw() should be reviewed... specially alpha blending...