This implements the solution to #25477. Any ``include`` directives
within state files can use multiple dot notation (influenced by Python
relative imports) to refer to a parent state.
This also implements the same functionality inside the stateconf
renderer
(http://docs.saltstack.com/en/latest/ref/renderers/all/salt.renderers.stateconf.html),
which supported relative includes, excludes, and prefixed states. This
PR expands on existing tests for stateconf.
This also updates the documentation accordingly.
