Using normalized [0..1] input points

...and improved mouse gestures support
Some testing still required...

Required by ProcessGestureEvent()

Mouse input is interpreted as touches to allow mouse gestures
detection... and get an unified inputs system for all platforms!

Removed GLEW external dependency, now it works with GLAD
Kept GLEW path, just in case... detected weird behaviour when testing
with gDEBugger

Added support for single header implementation and also inline functions
support

- Added function WorldToScreen(...).
- Added world to screen example.
- Review GetMouseRay() comment.
- Removed deprecated lighting functions from raylib header.

Simplified for the user (more intuitive and clear)
Removed lighting module dependency

- Fixed GetMouseRay() function.
- rlglUnproject() unused.

- Fixed Android locking screen bug. OnDestroy() was called when locking
screen.
- Power button input must be handled by OS.
- AndroidManifest.xml is affected by configChanges="screenSize".
- Updated library header for android template.

- Added functions for detect when pressed, during down and when
released.
- Added defines for back, menu, volume up and down button numbers.

Two new functions added to save/load values as binary data:
- StorageSaveValue()
- StorageLoadValue()

Corrected Android processing for some inputs (BACK button, VOLUME
buttons)
Redesigned Gestures system (some work still required)
SetEnabledGestures() - Only support desired gestures (requires some
review)

BeginDrawing() function with extended parameters

Required gestures module when compiling for Android and Web

[rlgl] Extensions strings loading was redone to avoid a Segmentation
Fault on Raspberry Pi

Added window drop files support

Shader functionality owns to rlgl, not core module

Corrected shader version depending on OGL version
Corrected bug in gestures module