Added custom token and reposelection support

A repository can now be chosen, so it is possible to execute
the changes command as a single command.

$changes [path]

Setting another changelog token is now supported:

$changes [path] --token <customtoken>

To limit the number of change events and for testing paging support,
it is possible to pass the maximum number of events for this request:

$changes [path] --max-results <unsigned int>