Command line interface + ORM module generator

[mesozoic]

This branch introduces a pyairtable command line script (which is only usable if additional optional dependencies are installed) for performing basic requests against the Airtable API. It also introduces a base orm subcommand which can generate a module with ORM classes using the metadata for a base.

Currently supported commands:

• whoami
• bases
• base BASE_ID schema
• base BASE_ID table ID_OR_NAME records
• base BASE_ID table ID_OR_NAME schema
• base BASE_ID collaborators
• base BASE_ID shares
• base BASE_ID orm
• enterprise ENTERPRISE_ID info
• enterprise ENTERPRISE_ID user ID_OR_EMAIL
• enterprise ENTERPRISE_ID users
• enterprise ENTERPRISE_ID group GROUP_ID
• enterprise ENTERPRISE_ID groups

This branch passes its own tests but has not been used in the wild, so I'll leave it up for a while as we test it internally.