Bump version to 0.2.1
Switch to using Sawyer

A lot of the code included in this commit came from Octokit
(https://github.com/octokit/octokit.rb/blob/master/lib/octokit/client.rb)
Document new response behaviour with Sawyer
Document body and header parameters
Fix minor grammar error
Get rid of #default_method method, and temporarily remove #user_agent
Clarify inspiration taken from others
Add links to mentioned projects
Add awesome banner
Make banner point to project root
Parse queries and convenience headers for GET and HEAD methods
Use symbols instead of strings (for options)
Add methods for commonly used header types (closes #16)
Make some Request module methods private
Document default header type setters
Implement #last_response method for wrappers (closes #15)