Update documentation  (#277)
Update documentation  (#277)

* Modify command line options nomenclature -- rename option "zipinput" -> "input"

- rename related short name "z" -> "i"
- rename class constant "ZIP_KEY" -> "ZIP_INPUT_KEY" for legibility

* Update documentation in README.md -- add documentation for new option `exclude`

- change sample usage to emphasize use of local datasets

* Update documentation -- Provide more examples of usage
MobilityData/gtfs-validator,MobilityData/gtfs-validator,MobilityData/gtfs-validator,MobilityData/gtfs-validator