Added support for PNG image loading and texture display to the Androi…

…d, iOS and emscripten builds.

* Added libpng for Android, iOS & emscripten, and libzlib for emscripten.
* Add buffer, file, image, shader, and texture utils.
* Add logging utils.

README.md and LICENSE.txt for GitHub commit.

Clean up formatting

Logical rearrange of methods + line breaking + cleanup.

Add 	'opengles-2' to UIRequiredDeviceCapabilities.

Create Makefile for emscripten and add .gitignore files