Renamed FontAtlas to Fonts. Further cleanup/comments.

ImFontAtlas allows loading multiple fonts into same texture. Revamped new init API for 1.30

Removed PixelCenterOffset, uncesssary

Merge remote-tracking branch 'upstream/master' into 2015-01-truetype ...

Conflicts:
	imgui.cpp
	imgui.h

Examples: Added a color slider for the background color + tweak first example use of button.s

ImFont::GetTextureData API allow to retrieve 8/32 bits data + lazily load defaults font ...

Examples: OpenGL3 and DirectX11 back to using 32-bits texture solely for
ease of integration.

Mde it optional to new() io.Font - however it stills needs to be loaded.

Examples' Says "OpenGL2" vs "OpenGL3" in title bar.

TAB to spaces

Speculative fix for warnings for GCC/Clang

Examples: all supports TextureID in renderer, added LoadFontTexture() function.

Loading TTF file with stb_truetype. Broke setup API slightly. Font baked, packed with space for custom data. Embeds compressed ProggyClean.

Examples: Fixed warnings for Clang

Examples: Added STB_IMAGE_STATIC in examples to avoid conflicting implementation. Relate to #109

OpenGL3 example: fix growing of VBO

New and better Set[Next]Window(Pos|Size|Collapsed) API. ...

Removed rarely useful SetNewWindowDefaultPos() in favor of new API.

OpenGL example: allow resizing window.

OpenGL3 example: fixed mouse handling.

Fix Clang warning with offsetof() macro? Added -Wall in OpenGL 3 example.

OpenGL3 example: unregistered mouse callback for mouse click-release faster than frame interval.

Examples: DirectX11: moved shader to be close to its usage location,

Examples: OpenGL3: cleaned up to match features of OpenGL2 example

Examples: adding title to the top of each examples. Cleaning up file headers.

fixed indentation mix, removed some unused code, updated different callback using the example_opengl code.

added opengl3 sample, mix from @ocornut and @thelinked