Standardize 'market' parameter across Web API endpoints

[sonallux]

Many endpoints of the Spotify Web API do allow to specify a 'market' query parameter. But the usage of this parameter is not equal across all endpoints, as some endpoints explicitly require the 'market' parameter and others do not. For example, the Get a Playlist's Items endpoint does require the 'market' parameter, but for the Get an Album's Tracks endpoint the parameter is optional.

To simplify the Web Api I would propose to standardize the usage of the 'market' parameter across all endpoints by making the 'market' parameter optional everywhere. The endpoints that currently require, that the 'market' parameter is set, should then assume the magic value 'from_token' if the parameter is not specified. This should match the behaviour of the endpoints that currently do not require the 'market' parameter, according to my experience with the Spotify Web API.