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.
* Added missing docs for public methods or functions.
* Made private methods or functions that didn't need to be exposed.
* Cleaned up spelling and grammar on some of the docstrings.
* Flags with empty values are considered not having a value they are set to.
* Json outputs empty values as null.
* Env ignores variable with empty values.
