The build and validate commands now take a list of files to process.
The outputs for files that specify the are given the same name as
the containing file with the extension changed to the extension that
the converter specifies.
* Got rid of LocatedNode since it was the same thing as Positioned.
* Positioned has a constructor now.
* Cleaned up some unnecessary macros.
* Created some more macros to make code more compact.
* Ran cargo fmt
* Some fixes to the README.
