Merge branch 'master' of github.com:maciekrb/mapreduceutils

Fixes bug with no results (NdbQueryModifier)

Adds structured property support and modifiers

- Enhanced DateFormatModifier now receives a "locale" argument to return
  names in the provided locale
- DateFormatModifier can now receive date_format in LDML
- Added DaysInMonthModifier to get the days in a month defined in a date
  or datetime
- Added NdbKeyIdModifier to generate ndb.Key(...).id()
- Added NdbQueryModifier to perform a query based on model params
- Added unittests

Fixes pipeline based unittest using cloudstorage writers

Implements Dict Record reader and fixes unittests

Optional flags allow to convert python NaN to null in JSON writer

Zero value exceptions now return float('NaN')

Implements default values and error handling

- Default values can now be provided when a property does not exist
- When a modifier method is not defined, modifier syntax can be used to rename properties
- Implemented error hangling for common cases (skipping records)

Unified MapperRecord + JSON and mapper keys

- Implements unified interface for ndb, db and JSON
- Implements mapper keys
@todo
Review matches_property_filters code

Added urlsafe() serialization to compare ndb.Key values