Merge pull request #2 from JMPerez/master

Ignoring some files that are not needed in the npm package
Add getPlaylistTracks
Update to version 0.0.6
Add fields parameter to retrieving tracks in a playlist
Update to version 0.0.7
Make minor tweaks to documentation
Add scopes to client credentials and search example.
Update test to reflect changes in error response
Can set position when adding tracks to a playlist
v0.0.8
Add related artists endpoint
Rename scope to playlist-modify-public

Spotify's Web API has renamed the `playlist-modify` scope to `playlist-modify-public` to better describe what it allows. Even though the old one will be supported for some time, the new one is the preferred way to go.