habanero v1

• fixes to docs/contributing.rst and package level docs for habanero (#89) (#90) thanks @Daniel-Mietchen !
• fix limit and offset internal handling for request and Request (#91) thanks @Bubblbu !
• content_negotation throws warning now on 4xx/5xx status code to allow for bad DOIs alongside good DOIS (#92)
• add example to README for querying works by DOI (#93)
• fail better when json is not returned; try json.loads and catch ValueError (JSONDecodeError is a subclass of ValueError) (#97)
• funders, journals, members, prefixes, types and works gain warn parameter to optionally throw a warning instead of error if a DOI is not found - not found DOI with warn=True returns None (#69)