Add POST, HTTP Basic Auth examples to README

This commit adds basic examples of how to make a POST request and how to
use HTTP Basic Authentication to the README.  This will help newcomers
handle common cases more easily.
Add Github-Markdown syntax highlight to README

This commit converts the example code in README from regular Markdown to
Github-flavored Markdown with syntax highlighting.  See:

https://help.github.com/articles/github-flavored-markdown
Merge pull request #11 from framed-data/readme

Add POST example, auth example, syntax highlighting to README