Add doc
Enhance Input constructor
Enhance constructors in pade.job module
Pass settings in to constructor of Settings
Add option to dump out sample indexes
Add some 'parents' for argument parsers

This lets us avoid repeating argument definitions
Add 'limit' arg to pade.job.Input.from_raw_file

This lets us only import the first N rows from the file.
Add --sample-indexes arg
Add summary class
Change makesamples to print group sizes