Support creating, fetching, and deleting filters

[iloveitaly]

Enhancement description

I want to be able to pull saved filters via the API

The problem it solves

Allowing users to reference the saved filters in their apps. Ex: https://github.com/iloveitaly/todoist-scheduler

Alternatives

We can use the sync API now, but it's not supported in these bindings #98 (comment)

Use case / screenshots

Additional information

[goncalossilva]

One of the reasons this isn't done is that we don't have dedicated APIs for creating, reading, updating, and deleting filters. That can be done via the /sync endpoint, but that's not ideal to be consumed from an SDK.

We should add dedicated API endpoints first, and then it becomes trivial to add them here.