define features returned by the API endpoints

[ingoboerner]

I went through the features of the DraCor API as described in the CLS INFRA report and checked which of them can be repurposed for the EcoCor API: see https://docs.google.com/spreadsheets/d/1lqgKB3Q79PIcW4k9nZUVund0Y7PypNaESp6zmFvOrzM/edit?usp=sharing

[ingoboerner]

• get metadata on all corpora (/corpora)
• get metadata on a single corpus (/corpora/{corpus_id})
• get all texts in a corpus (/corpora/{corpus_id}/texts) – the famous "corpus table" could be retrieved by requesting Accept text/csv with the request header
• a single text (/corpora/{corpus_id}/texts/{text_id}) – this endpoint would return either TEI-XML when requesting Accept application/tei+xml or the metadata on a text as JSON (Accept application/json),
• and, finally, /entities with filters as query params for all ecocor related entities/frequency stuff