Fix for issue #19
improved a bit saving references in embeddeds
updated travis config
forced to install the mongo driver in travis
posibilidad de pasar opciones al command  mapreduce y distinct

esto nos permite pasar, ahora mismo, un timeout
added tests for repository distinct & map reduce options
added to be able to customize the comparison of field values
changed to check in field values objects with double equal
refactored command in repositories
used collections distinct method
#4 Improved findByIds cache
improved repository findById
Fix #4 Empty groups read more than once
fixed cs
refactored cache tests
added lazy cache
fixed lazy cache call delegate set
fixed cs
Fix enforcing maps

- properly distinguish between referencesOne and Many
- enforce values only if proper reference exists
Merge remote-tracking branch 'upstream/master'