typo fix
Added CmdPathElem.__setitem__
Added more tests for CmdPathElem.__sub__
GenericCmdPath and their instances, no longer depend on
librouteros.dictdiff.
GenericCmdPath do not need to know anything about kes. Comparison logic
is moved to CmdPathElem.
GenericCmdPath.decide is now usable for all subclasses.
Updated unit tests to follow new code.
Added repositories for every known command path type. This will give
extendability and interchangeability.