Create an additional .getId() method to support getting resources by ID

Why

We currently support passing an ID to the .get(type, filter) method's filter parameter to request a single resource. #14 would allow a list of IDs to be supplied here.

For the farmOS 2.x API, filters should really be renamed to params. This is because JSON:API supports many additional features via query params: Filtering, includes, pagination, sorting, revisions and translations. Notably, some of these features apply when fetching even a single resources. For this reason I don't think we should accept an ID instead of a Dictionary (or object) of filter params; there are times when both parameters need to be supplied.

Another reason to move the ID to a separate method is because the response of a single resource is different than the response of multiple resources. Fetching a single resource, such as /api/log/observation/f1790e98-8762-4c16-bb93-ef53f0f77dfe returns a single object in the response data property. Fetching a collection of resources returns an array in the data property. This is change from the 1.x API where IDs were simply added as "filters". Previously when fetching a single ID via the client, the response would contain a list property of length 1.

The core JSON:API schema specifies that data can return a single resource, an array of resources, or null. Since POST, PATCH and GET to a single ID will always return a single resource in the data property we should provide proper return types for the API client methods that perform these behaviors.

Proposed resolution

Rename the filters parameter in all methods to params (or maybe options?)
Add an additional .getId(type, id, params) method for requesting a single resource by ID.
Re: #14, requesting multiple resources by ID can be done by providing the corresponding filter to the resource.get(type, filters) method. Example:

filter = client.filter('id', [id1, id2, id3], 'IN')
# the raw parameter would look like ?filter[id-filter][group][path]=id&filter[id-filter][group][operator]=IN&filter[id-filter][group][value]=[id1,id2,id3]
logs = client.logs.get('observation', filter)

farmOS / farmOS.py

Create an additional .getId() method to support getting resources by ID #42