Add GET path template for slot update using RFC 6570 § 2.4.2

[davidjsherman]

The REST verb for slot update is properly POST. However the Scratch protocol requires GET for all requests. So asebahttp accepts GET requests for slot update, with the value vector encoded in the URI separated by slashes. This variant needs to be documented in the api-docs.

Since OAS uses RFC 6570 path templates, in the general case we can use a composite value and rely on convention to encode the values: Q_set_odometer{/values*}.

When the slot is an event and we know the parameter names, we can instead expand the values explicitly: Q_set_odometer/{angle}/{x}/{y}.

[davidjsherman]

Fixed for variables in a944eef.