Merge pull request #51 from TS-RTX1911/master

opengl_example shared makefile for Linux and MacOSX
OpenGL example: Tentative fix for missed tap-to-click events on MacBook trackpad
OpenGL/DirextX examples: comments and tweaks.
Added SetKeyboardFocusHere() to set focus from code. Fixed tabbing through tab-disabled fields.
SetKeyboardFocusHere() sets focus on next widget instead of previous + works on tabbing-disabled widgets
SetKeyboardFocusHere() allow for an offset to access sub components + comments
Merge pull request #1 from ocornut/master

Merge