Make .gitignore file application specific

Use global ~/.gitignore for .swp, .bak, etc.
Clean up .gemspec & version

The gemspec starting point expects modern versions of ruby and has as few
dependencies as possible (just oauth2)
Update MIT License
Clean out unnecessary files

Will probalby re-add many when it's time. But for now they are adding
clutter.
Add organizational spec stubs
Add in first tests
Implement Configuration class & update Rakefile
Update Readme & sketch out usage
Flatten specs
Add OAuth spec and update gemspec to use rspec ~> 3.0
Implement LinkedIn::OAuth2 to make tests pass
Add YARD and consolidate test constants
Config and OAuth initialization tests pass
Add #auth_code_url and tests
Add auto-gen "state" for valid auth_code_url
Add initial API model
Add specs for access token retrieval
Add VCR recordings for access code success & failure
Document OAuth2 public class methods
Make get_access_token return new LinkedIn::AccessToken object