Better support private repos for organizations

[ryansb]

trafficstars

Using https://api.github.com/users/{SOMEONE}/repos endpoint does not seem to return private repos for an organization. In this PR, I added a --org option to match the one on the pull-requests command and allow collecting private repos.

This differs from https://github.com/dogsheep/github-to-sqlite/pull/76 in that it does not require all targets to be orgs or users.

Usage:

github-to-sqlite repos github.db user1 user2 --org org1 --org org2

[DonDebonair]

I would love this to be merged. I was hoping to use github-to-sqlite to analyze activity on repos across a Github organization. That is currently not possible