Mongoengine-migrate

Changed
- Fix AttributeError: GEOHAYSTACK (48) by [Mohsen-Khodabakhshi](https://github.com/Mohsen-Khodabakhshi)
- Fix Error when changing reference field to generic reference field (50) by [prihoda](https://github.com/prihoda)

Added
- Add additional functional tests for actions
- Indexes support (14)
- Write documentation (13)
- Add pre-push githook

Changed
- Fix command name in README by [rightplace](https://github.com/rightplace)
- Fix email check regex in EmailField (24) by [vmdhhh](https://github.com/vmdhhh)
- Fix `parameters` constructor argument gets to schema in `Schema` object (33) by [vmdhhh](https://github.com/vmdhhh)
- Seek module in current directory for `makemigrations` command (21)
- Fix "unhashable type" error in `AlterField` while making migrations (37)
- Prohibit renaming document to embedded document and back while making migrations (22)
- Fix `TypeError` raising in RunPython python expression printing method

Changed
- Change parameter dummy_actions to schema_only (1) by [dameyerdave](https://github.com/dameyerdave)
- Fix debug output if no last migration by [dameyerdave](https://github.com/dameyerdave)

Changed
- Fixed CI/CD and package building

Added
- Implement FallbackDocumentUpdater for perform an action in python loop when MongoDB version
below minimal for query
- Add python loop update callback where version of MongoDB is restricted to minimal
- Implement migration policy
- Implement Generic* fields
- Add and setup Travis CI/CD
- Add tox test runner

Changed
- Change class_filter build which is used for Document inheritance
- Flush schema to a db after every action completed instead of after whole action chain
- Fix inserting 're' module import statement in migration files
- Print warning if different documents use the same collection
- Print warning if collection in base and derived documents are different
- Improve convertion matrix
- Fix converters idempotency
- NamedTuple method declaration workaround for Python 3.6
- Fix change_dynamic method to use by_doc callback
- Rename --schema-only to --dummy-actions cli parameter
- Fix EmailFieldHandler.change_domain_whitelist method signature
- Implement change_inherit methods in actions
- Fix retrieving update paths for non-embedded documents in DocumentUpdater
- Using separate mongo connection for bulk writes
- Write only actually changed documents during update_by_document execution

Removed
- Remove isinstance dict checks from by_doc callbacks

Added
- Implement geo fields
- Implement convertion of legacy coordinates pair to/from GeoJSON fields
- GridFS fields support (FileField, ImageField)
- Implement embedded fields updater (actions, field handlers, type_key converters)
- Implement Database query tracer
- Make Schema class as interface to schema dict
- Implement AlterDocument action
- Document inheritance support
- Improve logging and add log levels. Print queries using logging in "dry run" mode
- Dynamic documents support

Changed
- Make ListField.max_length schema key as optional
- Change action chain build algorithm to iterate on actions instead of collections
- Setup Actions priority
- Substitute embedded documents before collections in actions chain
- Rename *Collection actions to *Document
- Define order of document types processing
- Add __all__ to python files
- Reraise SchemaError exception for any exception arisen in Schema class
- Fix fields updating in field handler methods, converters

Removed
-- Remove AlterDiff which was used in Alter* actions to keep parameters diff