Ftrack-query

Fixes
- If the primary key query finds multiple entities with different capitalisation, return the one exactly matching the input

Changes
- Remove `FTrackQuery.exc` (`ftrack_api.exception`)
- Remove `FTrackQuery.symbol` (`ftrack_api.symbol`)
- Remove `FTrackQuery.Entity` (`ftrack_api.entity.base.Entity`)

Features
- Add `startswith()` and `endswith()` operators

Changes
- Added error message if attempting to use `__contains__()`.
- Increase number of pre-defined primary keys

Fixes
- Fix error if no arguments are passed to `in_()`

Features
- Split `base.py` into `abstract.py` and `utils.py`
- Moved `FTrackQuery` from `query.py` to `__init__.py`

Improvements
- `and_()` and `or_()` will skip any `None` inputs

Fixes
- Fix error when closing session in debug mode
- Fix potential error when using `asc()` and `desc()`

Features
- Event class
- Update to Python 3

Improvements
- Add `__call__` method to entities as an alternative to using `__eq__`
- Automatically remap query to use IDs if passing list of entities into `.in_()`

Fixes
- Inverting a query will now correctly recalculate the order of operations
- Speech marks are now escaped in strings

- `not_` function added.
- Reversing a reversed query will now un-reverse it.