Invalid JSON body makes server crash + other possibly backportable things from express-pouchdb

[marten-de-vries]

An express-pouchdb issue that will crop up in pouchdb-express-router as well:

pouchdb/express-pouchdb#159

Includes a fix.

[marten-de-vries]

Two other issues that affect pouchdb-express-router as well:

• JSON body parser has a hardcoded limit of 1mb express-pouchdb#168 (although there's no config in pouchdb-express-router, so not sure how to fix. Probably just by increasing the limit.)
• Support for viewCleanup() express-pouchdb#165 (needed for the mapreduce test suite IIRC)

[marten-de-vries]

Better (and simpler) error handling for changes() would also be a nice thing to copy from express-pouchdb: pouchdb/express-pouchdb@0325f8b

There have been other improvements with respect to CouchDB compatibilty as well in core functions (bulkDocs, allDocs, attachments, compact), but I guess those aren't strictly necessary when the only goal is PouchDB interoperability.