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() ?

REVIEWED: ImageDrawRectangle()
ADDED: ImageDrawRectangleLines()

By default, internal white texture was used to draw most of the shapes; some time ago, support for white font character from default internal font was added. That way, all basic drawing (shapes, text) could be performed without a texture change and in a single drawing pass.

Now, we move a step further and we allow configuring the texture (and rectangle) used to do the shapes drawing.

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

- Updated dr_mp3 and implemented it
- Reviewed sampleCount vs frameCount
- Reviewed XM playing (some weird things...)

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.

Why am I still supporting this???

...disposing RenderTexture.

Loading full mp3 file works but loading for music streaming does not work, it seems total number of samples is not obtained correctly from mp3 file...

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.

OPENGL_VERSION is the version requested by the user,
not the detected one...

Fixes #660.

GenImageFontAtlas() allocates an array of stbrp_rect for the packing functions, but it never frees them.

The prototype of GenImageFontAtlas() in the main raylib.h header has a set of swapped parameter names.
Going through the usage of the function within raylib itself, it appears as if the correct order is:
1) charsCount
2) fontSize

However, it's exposed to the world as the other way around, which may cause some major confusion.

Generating the projects using CMake, targeting VS2017, results in an error when compiling.
This is due to physac.h trying to make a 'vertices' array of size 'int count', making it const does not work, either.

This changes the static declaration to a malloc/free combo.

Tested using the physics-demo.