Add monsters API

[osrsbox]

The last update to adding support for monster data was building the monster JSON schema, closed in PR #134. The next logical step is to build the monsters API for use in the osrsbox package to access monster data, as well as to help build the monster database (populate the Python objects and export to JSON).

This involves:

1. Add monster API under osrsbox directory. Have a monster_definition for base properties, and a monster_drop for monster drops - each stored in a dictionary and populated into a list. There should also be a all_monsters module for loading the monster data.
2. Remove the monsters_api folder from the osrsbox package, so that the code isn't included with the PyPi package until the monster data has actually been added.
3. Test the API with some faked data.
4. Test the API/faked data with the JSON schema and pytest test monsters module.

EDIT: Although not specifically stated, this does not include the monsters_builder component to actually build the monster database. That will be the next logical step.

[osrsbox]

This has been added... see #16 for information.