Not supported for the moment, issues with Linux (symbol `Font` redefined) and OSX (NSGL type redefined)

REVIEW: Reorganized global variables for consistency
ADDED: GetWindowHandle() to get native window handle
ADDED: GetDirectoryFiles() to get files list for a DIR

Apple ought to fix their OpenGL implementation, but with OpenGL now
deprecated this might not happen.

This has been reported upstream in GLFW in glfw/glfw#1334.
The workaround comes from kovidgoyal/kitty@b82e74f99

This also fixes the HiDPI (Retina) scaling issues reported in #497,
so the workaround is enabled anywhere __APPLE__ is defined.

- Using same idea as SetWindowMonitor to take in a index with 0 being the primary monitor.

- Added else so return not compiled twice.

- Added PLATFORM_DESKTOP check for Monitor functions to try to fix issue on android.
- Not sure what return types should be when not on desktop. Added rough guess for now.

- Fixed tabs used instead of 4 spaces

- Get number of monitors
- Get size, physical size and name of primary monitor. Could pass monitor id instead not sure.

REVIEWED: ExportImage()
REVIEWED: ExportMesh()
ADDED: ExportWave()
REMOVED: Internal funcs: SavePNG(), SaveBMP()

NOTE: These changes break the API (parameters order)

Some minor tweaks around

strprbrk() does not follow raylib function name convention but as it is
very similar to the standard strpbrk(), we'll keep the naming... also,
don't like to mix static functions with API functions but as strprbrk()
is just used in the two functions below, it's ok to be there... maybe it
could be refactored in a future or even move the logic inside the
required functions...

Noted in #634.

Fixes #634.

PLATFORM_WEB is not the only platform that doesn't define
GLFW_TRANSPARENT_FRAMEBUFFER, it's also recent enough that it's not
included in the most recent GLFW 3.2.1 release, so this error can creep
up when using USE_EXTERNAL_GLFW.

Examples can be compiled for web with no code change at all! Usually
examples need to be refactored for web... using emscripten code
interpreter (emterpreter), it can manage synchronous while() loops
internally... as a downside, execution is very slow...

This change allows rlgl.h usage as independent single-file header-only module... still some tweaks required, like removing GLAD dependency... required extensions could be manually loaded!

Also removed shader_distortion.h, embedded in rlgl.h

Joystick support is not implemented just yet, not difficult but it
requires some work...

...by emscripten glfw javascript implementation

Try to avoid types conflict with Font

- Renamed Begin3dMode() --> BeginMode3D()
- Renamed Begin2dMode() --> BeginMode2D()
- Renamed End3dMode() --> EndMode3D()
- Renamed End2dMode() --> EndMode2D()

Allow compiling the library with support for automatic screen capture
(KEY_F12)

Added raylib version to config

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).

Reviewed for PLATFORM_ANDROID and PLATFORM_UWP

This is already the order that is used for Android. It doesn't appear to
make a difference on desktop but on web using the timer before it's been
initialized (by glfwInit, inside InitGraphicsDevice) causes the a long
(and variable but often several seconds) sleep between the first and
second frame.

Fixes: 468309d ("Early-exit InitWindow if InitGraphicsDevice fails")

Changes motivated by commentary in pull request 513

Inspired by #504.
Instead of requiring the user to do PLATFORM_ANDROID #ifdefery,
have the android_main entry point exported by raylib and call
the user-defined main. This way many games could (in theory)
run unmodified on Android and elsewhere.

This is untested!

- SetWindowSize() to scale Windows in runtime
- SetMouseScale() to scale mouse input, useful when rendering game to a
RenderTexture2D that will be scaled to Window size (used on rFXGen tool)

GLFW has been updated to latest version, probably this code is not
required any more due to already been integrated into library... but it
needs to be tested...

RAYMATH_EXTERN_INLINE was renamed to RAYMATH_HEADER_ONLY, which user code
may define if they want to use it as header-only library. If multiple
files in the same project define RAYMATH_HEADER_ONLY, they might each
have duplicate out-of-line definitions of the same functions.

By default, raymath.h exposes inline definitions, which instructs the
compiler _not_ to generate out-of-line definitons, if out-of-line
definitions are required, those of the file defined with
RAYLIB_IMPLEMENTATION are used instead. There may be only one such file.

In C++ mode, the compiler will select only one out-of-line definition
automatically, so no need to define a RAYLIB_IMPLEMENTATION.

Unfortunately, we have to remove raymath function declaration from
raylib.h as those declarations would lead to duplicate out-of-line
definitions which would yield linker errors. This problem didn't
exist with GNU89 or C++, because there multiple defintions are ok,
but in C99 they aren't.

This reverts commit 6ffc8cb799.
and commit e4d7bbec1e.
which I pushed by mistake...