vet-bot: Command-line args to run against a single repository

[kalexmills]

By default, vet-bot runs in 'scrape mode' -- it samples from a list of github repos and visits them, parsing the code and running the analyses.

A command-line argument should be introduced which changes its operation to scrape a single repository given as a command-line argument. Example usage:

vet-bot scrape kalexmills/bad-go

The default usage could also be replaced by:

vet-bot sample all-repos.csv

which could continuously sample from the all-repos.csv file and output the list of visited repos in all-repos_visited.csv.

[kalexmills]

Realized what I'm doing doesn't actually involve this issue (though it easily could).