For upcoming premium features

Adds get previous line comparison uris for GitHub
Improves perf of get previous comparison uris for GitHub
Replaces HEAD usage with proper revision for GitHub
Renames comparison uri methods for clarity

Adds authors filtering to commits

Splits get commit branches into 2 methods

Consolidates into a single method call

Adds unit testing (just for the trie for now)

Consolidates to node-fetch 2.6.7 as Octokit requires v2

Moves eslint ignores into rc file
 Removes unused dev dependency

Giving up on better else/catch/finally formatting -- can't fight anymore
Switching to tabs for better accessibility
https://twitter.com/sh4na/status/1146837957200027648