Turn couch_doc_json_tests into unit tests
Turn couch_doc_json_tests into unit tests

There are two issues:
1. There is no any reason to start server instance to ensure that we
accepts valid decoded JSON objects and throw right errors on bad ones;
2. Tests get actually executed before setup/0 call

fkaempfer/couchdb,apache/couchdb-couch,apache/couchdb-couch,cloudant/couchdb-couch,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,cloudant/couchdb-couch,cloudant/couchdb-couch,fkaempfer/couchdb,apache/couchdb-couch