Add initial structure for jsonfmt.py

Haven't found any JSON formatters that use the style I want by default,
so I'll create my own.

4ab64204-4a83-11e4-b146-c80aa9e67bbd
jsonfmt.py works, uses only stdin/stdout atm

ed9b3f9c-4a83-11e4-814a-c80aa9e67bbd