Rewrite of networking_101, generic cleanup (typos)

First attempt at a pull request, couple of things for consideration:

- There are some updates with large To Dos left. Rather than just leave them stale in my working copy and have to deal with merging later, I'm committing them now. If this isn't the done thing - my bad! :)
- This is my first pull request and update to OpsSchool stuff, so if I'm not hitting the right kind of writing style, please shout and I'll update

Changes to consider:

- Rewritten networking_101 a little to hopefully clarify out IPv4/IPv6 a bit more, but merged in the TCP/UDP changes.
- Added self to contributors
- Updated formatting in a few places
- Added in hyperlinks for subreddits
- Couple of minor updates (typos)