Final docs and audit cleanup

[Mr0grog]

This is the last bit of cleanup I wanted to do to close out #191. There are a few overlapping things here (let me know if I should pull any of these out):

• Added more detail to CONTRIBUTING.md about required versions, manual testing and debugging, etc.
• Fixed assorted typos, minor grammar things, marked up inline code snippets and symbol references as code, made issue references into links, made directory references consistent (e.g. lib/ vs. /lib), etc. in docs.
• A few more dependency updates to clear all the remaining audit issues.

[pimterry]

Nice work, thanks! These all look like great improvements :+1: