Dataql

Added
Small updates for `graphql-server`

- Subclasses of `NamedArg` can now customize the operator
- Use the term "coerce" instead of "cast"
- Add a parent class for all resources & co

Fixed
- Make functions work in EntryPoints

Fixed
- Package is now installable!

Added
- Manage `None` values (abort filtering, etc, ans simply return `None`)

Added
- Ability to use standalone functions in addition to attributes.
- Better management of instances of objects with a `__call__` method.
- Add a `run_tests.py` file.
- Allow using spaces around colon when naming a resource in a query.
- Better exceptions
- Manage slicing/list indexing in filters
- Change in the format for lists, allowing to return list of values, not only list of dicts
- Access allowed dict items

Changed
- List format in query language

- First working version