feat: implement search on entities

[ritiek]

Status for all musicbrainz entities that implement search:

• Area
• Artist - was previously implemented
• Event
• Instrument
• Label
• Place - There's some inconsistency in the API response which I reported here. We should probably wait before implementing this and see maybe see if this can be resolved from the musicbrainz side itself otherwise we'll have to workaround this in our library as we currently parse the coordinates as f64 which fails when attempting to use the same coordinate struct to also parse the search response.
• Recording
• Release - was previously implemented
• Release Group - was previously implemented
• Series
• Work
• Annotation
• Tag - requires http digest authentication which isn't implemented at the moment (e.g. open this while you're logged out of musicbrainz.org). Tag search will need to be implemented once we have authentication up in musicbrainz_rs.
• CD Stub

Addresses #23.

[ritiek]

@oknozor I haven't implemented search on place and tag entities for the reasons mentioned in the PR description, otherwise this should be ready for review!