Add support for URL lookup and browse requests.

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>
Deduplicate relatable types into a RELATABLE_TYPES list

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>
Add 'area' to the list of relatable types.

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>
Update docs.

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>
Extend relation includes to browse requests generally, as the server supports this

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>
Merge branch 'relatable-type-deduplication'

* relatable-type-deduplication:
  Extend relation includes to browse requests generally, as the server supports this
  Add 'area' to the list of relatable types.
  Deduplicate relatable types into a RELATABLE_TYPES list

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>
Merge branch 'url-lookup'

* url-lookup:
  Update docs.
  Add support for URL lookup and browse requests.

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>

Conflicts:
	musicbrainzngs/musicbrainz.py
Fix whitespace.

Signed-off-by: Ian McEwen <ianmcorvidae@ianmcorvidae.net>