Fixed hold gesture detection

- Fixed gestures hold detection.
- Improved hold state detection for little touch position increments
(sensitivity).

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

Added ray-sphere collision detection

This reverts commit 423a45ac85.

Added support for single header implementation and also inline functions
support

- Added simple ray-sphere collision detection.
- Added extra function with extended parameters to obtain collision
point vector.
- Fixed bounding box calculations init values (were causing compiling
errors).

standalone raymath

look over for errors

Moved building information to raylib github Wiki page

Reviewed vertex type variables

World to screen conversion and little review

- 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

... transparent elements

Fixed small glitch on zoom-in

It seems that now works. Tested all free camera features with some
directions and positions and no unexpected behaviours detected. I don't
know if those lines are really indispensable.

Implemented ray trace from mouse position

- Added CheckCollisionRayBox() function.
- Updated and improved core 3d picking example (currently working as
expected).

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