Add unit tests for getting existing docs.

https://github.com/couchbase/couchbase-lite-ios/commit/e0469300672a2087feb46b84ca498facd49e0066
Write example code for resolving conflicts.
Fix failure in the testResolveConflict test.  Add new test testDocumentChangeListener()
Issue #243 - add test to reproduce

https://github.com/couchbase/couchbase-lite-android/issues/243
Issue #243 - further checks related to canonical forms

https://github.com/couchbase/couchbase-lite-android/issues/243