Port FauxReader

* introduce PDAL_ADD_DRIVER macro that creates object library for the
  given driver
* 'drivers.faux.reader' becomes 'readers.faux'
* 'pdal::drivers::faux::Reader' becomes 'pdal::FauxReader'
* headers moved from ./include/pdal/drivers/faux to ./drivers/faux
* source moved from ./src/drivers/faux to ./drivers/faux

If we like this new structure, additional drivers/filters can follow.