Create Revision from JSON

- Create factory method to create document revision from downloaded JSON
  data from CouchDB/Cloudant.

- Created CDTSavedHTTPAttachment which represents a HTTP accessable
  attachment, this can either be in CouchDB/Cloudant or a generic
  datastore.
Merge pull request #56 from cloudant/34404_create_rev_from_json

34404 create rev from json
Updates to documentation

Update conflict resoution documentation to make it clear that
CDTMutableDocumentRevisions can be returned in conlfict resolvers.
Merge pull request #67 from cloudant/35676_update_docs

Updates to documentation
Adds TDInternalErrorDomain and error code for when local
database is deleted during replication.

TDReplicatorManager sets TDReplicator's error property
with appropriate NSError when local database is deleted.
Adds error property in CDTReplicator for error information retrieval
by objects other than the delegate.

The error is translated from TD* level error type to CDT* error
here (the location for this transformation may change
in the future). If the TD* level error is not specifically
handled, the TD* error is used. As of this commit, only
TDReplicatorManagerErrorLocalDatabaseDeleted is transformed to
CDTReplicatorErrorLocalDatabaseDeleted.

Fixes small bug in CDTReplicatorErrors enum where the value for
CDTReplicatorErrorTDReplicatorWrongType was incorrecly set to 2.
Fixes bug in CDTReplicator -stop. The state was incorrectly set to
the wrong value in a previous commit.
Adds the state of the CDTReplicator to the logging message at the
beginning of -replicatorStopped.

Removes an incorrect Warning found in -replicatorStopped.
Moves common code that tracks progress of replication and makes
calls to the delegate into a single method instead of repeating
that code in -replicatorStopped and -replicatorProcessChanged.
Adds tests to ReplicationAcceptance project for CDTReplicatorState when
local database is deleted during replication.