See https://github.com/raysan5/raylib/issues/686

Calling just `xdg-open` is not right. One needs to pack the URL in `'`.
If we don't do this then some special characters (like ampersand) will
be executed.

Maybe this is true for Windows and Apple case too, but I don't own any
such system. So please merge this, and if it's true for more cases let's
use `sprintf()` in the other cases too.

OpenURL() is a function that most games probably will never need.
Wasting 512 bytes to store of a static char to store an the URL is not
wise.

I propose to have it dynamic building the string on the fly.

Corrected bug on ImageDrawRectangleLines()

Some projects need the buffer to not be empited when drawing to the render texture. I would suggest making maybe a variation of the function if you'd like to keep backwards compatibility, maybe like: BeginTextureModeNoClear() ?

Wait for input events passively (sleep) instead of polling events actively every frame

text:     IsEqualText() -WIP-
audio:  SaveWAV()
audio:  ExportWaveAsCode()
textures:  ExportImageAsCode()

The comment sais it allows max 256 files, but the MAX_DIRECTORY_FILES
define actually is set to 512.

Let's have a seperate if linux block for this. Since we will need to
define MAX_FILEPATH_LENGTH for all other cases. And its more readable
like this.

On Linux systems the length of the path is defined in linux/limits.h as
PATH_MAX.
Lets use that for MAX_FILEPATH_LENGTH, which is a define that we can
find in some comments in the code that is actually never used. Instead
often we see 256 handwritten.
So lets have MAX_FILEPATH_LENGTH as a proper define, being set to
PATH_MAX on Linux and to 256 on Windows systems.

RENAME: GetLastWriteTime() to GetFileModTime()

- Added a function to get the last write time of a file. I used this so I can reload files or resources if the time since they were last loaded changes.

...and MacOSX OBJC types definition...

Expose native Cocoa Window again...

Could not be retrieved for now...

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