Also added new compilation FLAGS for that pourpose

That way, a user needs only to touch a single file to configure what
features raylib is built with.
Include guards are left out intentionally, because config.h should only
be included in source files, not headers.

Later on, config.h can also define the raylib version (#461).

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

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

Variable t was read and modified without interleaving sequence points,
technically undefined behavior. Report by Clang's -Wunsequenced

Added: DrawRectangleGradientV()
Added: DrawRectangleGradientH()

Moved function DrawRectangleT() from text module to shapes
Added some comments

Supports line thickness

Working in modules configuration flags...

Function names, code formatting...

raylib uses spaces between '+' and '-' signs but not between '*' and '/'
signs, it's a chosen convention

To get it, use GetDefaultTexture()

Depth test disabled for 2D and only used on 3D; consequently LINES vs
TRIANGLES vs QUADS buffers drawing order maters... but blending also
works ok.

- Removed DrawQuad() function
- DrawBillboard() uses DrawBillboardRec()
- DrawPlane() uses RL_TRIANGLES
- DrawRectangleV() uses RL_TRIANGLES, that way, [shapes] module uses
only TRIANGLES buffers.

Support multiple texture formats (uncompressed and compressed)
Postprocessing shaders support
Model struct redefined and improved
Extended loading functions for Textures and Models
Simplified functions: DrawPlane(), DrawQuad()
Deleted functions: DrawPlaneEx(), DrawGizmoEx()
Now Text module only depends on Textures module
Shapes: Reviewed functions to low lines/triangles usage
Removed useless tabs and spaces around code

Corrected some bugs on the way...
Automatically convert textures to POT on RPI and WEB

This is a huge update. Check CHANGELOG for details

Set default raylib to use OpenGL 1.1 (compatibility issues on ATI cards)

We have three vertex buffers: lines, triangles and quads for textures.
Drawing in a desired order could become a nighmare... noww it seems it
works prety well...

View CHANGELOG for a detailed list of changes

Nearly a complete rework of Models module
Some teaks on multiple functions