Fixes this build failure:
http://www.cpantesters.org/cpan/report/a069fade-0e1f-11e8-a1cf-bb670eaac09d

- Some functions renamed
- Comments reviewed
- Functions reorganized

Otherwise we may run into LoadDefaultFont and crash in rlLoadTexture
Also moves InitTimer() before InitGraphicsDevice(), to allow it to be
tested even if InitWindow ultimately fails.

Otherwise we run into an assertion failure inside GLFW's glfwGetVideoMode.
Example:
http://www.cpantesters.org/cpan/report/b4ba5894-0bdb-11e8-841e-2c60b04e1d2d

This is related to #456.

Allows loading of shader from text code string directly

Note that this version is under development and could be buggy on some
platforms...

In case graphic device could not be created it returns false instead of
failing with an error tracelog (and consequently closing the program).
Window initialization success could be checked with new function
IsWindowReady()

You can't do much with raylib if glfwInit or glfwCreateWindow fails,
currently it just exits by means of TraceLog(LOG_ERROR.
User code, however, might want to fall back to a text-only UI
or display a warning if raylib can't be used.

glfwSetWindowPos was called on a NULL window, triggering an assert
inside GLFW. Check for failure and exit cleanly by means of
TraceLog(LOG_ERROR instead.

-DWITH_SYSTEM_GLFW=ON: Link against system glfw and fail otherwise
-DWITH_SYSTEM_GLFW=OFF: Use embedded rglfw.c
-DWITH_SYSTEM_GLFW=IF_POSSIBLE: Probe for system glfw but fallback to
                                rglfw if unavailable

Also change Linux 64-bit CI build to install system glfw and use it,
so this doesn't bitrot.

Addresses #453.

Cherry-pick from upstream glfw/glfw#1196
Found in CPANtesters test of Alien::raylib:
http://www.cpantesters.org/cpan/report/d956d128-0339-11e8-b0d1-b6c4abd39192

Just in case ClearBackground() is not used after BeginTextureMode(), it clears fbo to color defined by previous ClearBackground()

which is the default behavior on C99 and up.

When changing image format, mipmaps are lost and regenerated from
scratch

Review rlLoadTexture() function to make it simpler, now OpenGL texture
glInternalFormat, glFormat and glType are retrieved with new function
GetGlFormats()

As an extension, GNU C treats sizeof(void) as 1. MSVC doesn't.
Make it an error on GCC/Clang to avoid accidental MSVC breakage.

GNU C allows it as a compiler extension, but MSVC doesn't.

- Support OpenGL 1.1 if selected macro
- Corrected MSVC compiler issues with (void *) data
- Removed raylib.dll project
- Created DEBUG_DLL and RELEASE_DLL configurations

Added support for noise image offset

- Added support for mipmap levels loading
- Removed internal function LoadTextureCompressed(), not required any
more...

- Renamed VERSION to RAYLIB_VERSION
- Renamed API_VERSION to RAYLIB_API_VERSION
- Renamed RAYLIB_RELEASE to RAYLIB_RELEASE_PATH
- Support Web Assembly compilation on PLATFORM_WEB

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!