Add example applications to O2 source tree

Added Twitter OAuth example
The new source tree will be as follows:
.
├── examples
├── LICENSE
├── README.md
└── src

src:
Contains O2 source code. This also has a src.pri which other Qt applications can include to access O2 files in their
project.

examples:
This dir will contain all demo examples for testing various OAuth features. Currently, it contains an example Twitter
application which authenticates using Twitter OAuth.

This commit only checks-in the CLI mode of the example application. A Qt Quick based GUI mode will be added later.