add supports of view changes in the _changes API
add supports of view changes in the _changes API

Now when the option `seq_indexed=true` is set in the design doc, the
view filter in _changes will use it to retrieve the results. Compared to
the current way, using a view index will be faster to retrieve changes.
It also gives the possibility to filter changes by key or get changes in
a key range. All the view options can be used.

Note 1: if someone is trying to filter a changes with view options when
the views are not indexed by sequence, a 400 error will be returned.
Note 2: The changes will only be returned when the view is updated if
seq_indexed=true

KlausTrainer/couchdb-couch,apache/couchdb-couch,smithsz/couchdb-couch,smithsz/couchdb-couch,cloudant/couchdb-couch,alanning/couchdb-couch,ngpestelos/couchdb-couch,cloudant/couchdb-couch,fkaempfer/couchdb,ngpestelos/couchdb-couch,smithsz/couchdb-couch,fkaempfer/couchdb,fkaempfer/couchdb,apache/couchdb-couch,fkaempfer/couchdb,KlausTrainer/couchdb-couch,cloudant/couchdb-couch,apache/couchdb-couch,fkaempfer/couchdb,KlausTrainer/couchdb-couch,ngpestelos/couchdb-couch,alanning/couchdb-couch,fkaempfer/couchdb,alanning/couchdb-couch