Add help information to option parser
Package into Python project

This adds a very minimal packaging scheme, copied from this tutorial:

   http://www.scotttorborg.com/python-packaging/minimal.html
Add a description string to help output
Replace optparse module with argparse

Optparse is deprecated, and argparse has support for positional
arguments.

Issue #1.
Remove redundant process invocation

This results of this first "trial run" are not being used anywhere.
Inject a command string into parse_args()

This adds a string "command" to the return value of
ArgumentParser.parse_args() which means that individual methods don't
need to concatenate the separate arguments themselves.
Refactor classes into separate source files

This creates per-class modules for each of the classes in srtime.