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.

Fixed Android bug and added physic buttons inputs

- 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()

Improved lighting and physac engine modules and added new example

New physics example to see AddForceAtPosition() behaviour applied to 5
rigidbodies.

- Improved physics calculations.
- Added AddForceAtPosition function (added to all enabled rigidbodies).
- Updated raylib header.

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)

...to avoid .mem file creation

Added LoadBMFont() to load AngelCode fonts (.fnt)
Implemented LoadTTF() to load .ttf fonts (crappy packaging)