api:v1: tidy up docstring and unneeded constants

A very minor set of tidy-ups to api.v1 which make the aim of the module
clearer in the docstring and remove the API_VERSION constant which is a
little redundant. Should other parts of the application wish to refer to
the API is should be via the exported api.v1.api object.
Merge branch 'api-refactor' into v2-playground