Check if provided path is a full path containing system root letter: C:\

Just for clarification, no plans to remove libc dependency, just did some code analysis to see how much raylib depend on stardard C library. My conclusions:

 - stdlib.h: primary dependency is for malloc() and free()
 - stdio.h: primary dependency is for FILE access, maybe it could go through a custom ABI?
 - string.h: just around 8 functions required
 - math.h: just around 8 functions required
 - others: 1-2 functions required for some other headers

Added SUPPORT_TRACELOG_DEBUG config

* [core] REDESIGNED: Implement global context

* [rlgl] REDESIGNED: Implement global context

* Reviewed globals for Android

* Review Android globals usage

* Update Android globals

* Bump raylib version to 3.0 !!!

* [raudio] REDESIGNED: Implement global context

* [raudio] Reorder functions

* [core] Tweaks on descriptions

* Issues with SUPPORT_MOUSE_GESTURES

* [camera] Use global context

* REDESIGN: Move shapes drawing texture/rec to RLGL context

* Review some issues on standalone mode

* Update to use global context

* [GAME] Upload RE-PAIR game from GGJ2020 -WIP-

* Update game: RE-PAIR

* [utils] TRACELOG macros proposal

* Update config.h

REMOVED: IsTouchDetected()

Now touch inputs scale proportionally to the canvas size

Addressing issue #1056

Allow frustrum culling near/far distance configuration at compile time.

* We get the video mode from the target monitor and use that to set, therefore
keeping windowed-fullscreen
* Added a GLFW_AUTO_ICONIFY 0 hint so that glfw does not minimize the window
when changing focus from a windowed fullscreen window. This is more expected
behavior for windowed full screen, when a user alt-tabs or clicks on a window in
the other monitor, they expect their windowed-fullscreen window to remaining up.

If press/release events for a mouse button come too fast, then using
`IsMouseButtonReleased()` does not work. This has been noticed when
using a touchpad on Linux when tapping with two fingers two emulate
right mouse button click.

The situation looks like this:

```
BeginDrawing           <-- current==released, previous==released
Pressed                <-- current=pressed
Released               <-- current=released
IsMouseButtonReleased  <-- returns false because current==previous
EndDrawing             <-- previous=released
```

The fix is to update the previous mouse button state in addition to
current mouse button state when `MouseButtonCallback()` is called by
glfw. Now the situation is as follows:

```
BeginDrawing           <-- current==released, previous==released
Pressed                <-- current=pressed, previous=released
Released               <-- current=released, previous=pressed
IsMouseButtonReleased  <-- returns true because current!=previous
EndDrawing             <-- previous=released
```

It seems to work ok on my old Intel HD Graphics card... it should work anywhere else

* fixes for switching full-screen and v-sync

* requireVsync flag

Keeping original API

* add api FIFO based character input.

* rename input character functions

* replace tab to space x4 #1012