Add search, similar and refactor object names

Artist and Track:
1. Get similar
2. Search

Album:
1. Search

Other changes:
1. Artist -> LastArtist
2. Album -> LastAlbum
3. Track -> LastTrack

Closes #13

EDIT:

1. Added the rank property for tracks.
2. The Largest property to the lastfm image set
3. Get info for an artist, album and track by mbid.
4. Pagination for the get top tracks and albums on the artist api
5. Added charts api (basic methods)
6. Fix parsing bugs (thanks to the damn unpredictable apis)