* (Issue 42) Include bson_id when serializing to JSON.
* (Issue 44) Required Fields with Default Values.
v.1.0.3, 2014-02-24 -- Forward Compatable Changes
* Dirty field checking
* Use "upsert" by default when updating
v.1.0.4, 2014-02-25 -- Forward Compatable Changes
* Test for Documentsave "upsert"
* (Issue 49) Problems with boolean fields
v.1.1.0, 2014-04-29 -- Forward Compatible Changes
* Uses MongoReplicaSetClient if hostname includes
"replicaSet"
* (Issue 51) Model level validations
* Add write concern option support for Documentsave
* (Issue 48) StringFields and non-string values
* Various documentation fixes and test clarifications
v.1.2.0, 2014-05-05 -- Forward Compatible Changes
* (Issue 3) Uniqueness Validation
v.1.2.1, 2014-05-14 -- Backwards Compatible Bug Fixes:
* StringFields can now handle values with unicode
characters that have been processed by a JSON parser.
v.1.2.2, 2014-10-23 -- Backwards Compatible Changes:
* If a tavi.Document is initialized with unknown
kwargs, log them and their values.
v.1.3.0, 2014-12-04 -- Backwards Compatible Changes:
* A compound unique index is created when multiple
fields are specified as unique in a document.
v.1.4.0, 2014-12-15 -- Backwards Compatible Changes:
* Add new ArrayField field type.
v.1.4.1, 2015-02-03 -- Backwards compatible Changes:
* BUGFIX: Don't use root logger.
* Update license copyright year.
* Minor test refactoring.