Implemented the following methods for the version 1.2 of 7digital api:
- artist/browse
- artist/chart
- artist/details
- artist/releases
- artist/search
- artist/toptracks
- artist/similar
- artist/tags
- artist/byTopTags
- track/search
- track/chart
- track/details
- track/preview
- release/bydate
- release/chart
- release/details
- release/recommend
- release/search
- release/tracks
- release/tags
- release/byNewTags
- release/byTopTags
- tag/list
Handle different api error message through meaningfull exceptions.