Pin FMDB version to 2.3
Remove deprecated APIs

- Remove deprecated APIs
- Remove legacy API mode to document update internals
- Remove usage of deleted APIs from Sample
- Changed the description property in CDTTodo to taskDescription to fix
  warning about property redeclaration (description is declared in
  NSObject)
- Changed test file names, removing suffixes indicting new API tests
- Updated CHANGELOG.md
- Created API migration document
Merge pull request #64 from cloudant/35676_remove_deprecated_apis

35676 remove deprecated apis
Modifies TDReplicator to report an error when a local database is deleted
during replication.

Error is propagated to CDTReplicator and reported by it's state.

Improves error reporting by ensuring that its errors are reported by
both by CDTReplicator -replicatorProgressChanged or -replicatorStopped,
but only if the transition is from an active to error state (so error
reporting to the delegate happens only once).

Exposes error property in CDTReplicator for error information retrieval
by objects other than the delegate. If we are reporting 'state' to objects
other than the delegate, it seems reasonable to provide access to
the error information as well.

Reduces redundancy of code by moving common code in CDTReplicator
-replicatorProgressChanged and -replicatorStopped to a common method.

Adds tests to ReplicationAcceptance project for CDTReplicatorState when
local database is deleted by a delegate during replication.