Fixed error : raise TypeError(repr(o) + " is not JSON serializable") , TypeError: ObjectId('') is not JSON serializable
Merge pull request #313 from delciotorres/master

The mongoengine auth example won't work TypeError and AttributeError
refs #3, fixed sqlalchemy.exc.DataError when saving empty AjaxSelectMultipleField
Merge pull request #314 from zavatskiy/issue_3

refs #3, fixed sqlalchemy.exc.DataError when saving empty AjaxSelectMultipleField
Add documentation for macro helper
Merge pull request #316 from ArtemSerga/parent

Add extra documentation for `column_formatters`