add a minimal command line arg parser

The default implementation from Nim parses `--flag:value` and `--flag=value` but doesn't allow `--flag value` which is what most people use.

- Either write a parser to support all three
- Use something like http://docopt.org/ , though this approach is secondary since, docopt + regex as inclusions will add up to the size of the binary which I want to avoid if possible

Start by reading Nim's default command-line argument parser and compare its handling of --flag:value, --flag=value, and --flag value. Review the docopt option as a secondary reference; done means supporting all three forms without unnecessary binary-size growth.

Written by the indexing model from the issue text.