Add RakeTest to the rakefile to support minitests.
Add pry as a development dependency for debugging.
WIP for better error management.

- This code could be simplified. Should use a closure to keep track
of retries rather than an object.
Further tweaks to the library.

- Add a new call to get user by login.
- Add better exception handling.
Bump up the version to 0.0.2

- Includes new user api call to get user by login.
- Better invalid token handling. Tries 3 times by default before
raising an exception.
- More explicit exception handling.