Update links to point to GitLab where possible

See merge request !132

Add more detail on Sodium

See merge request redox-os/book!131

Some links are not valid as they are only on GitHub (not part of our
team), other links are not valid as some contributors have not logged
into our GitLab yet

I also disambiguated the "Exploring Redox" title that was shared between
a page and a chapter

add packages needed for build

Gave a hint about adding xargo to the path

To help users who haven't previously installed software via cargo

added login information

Fixed typo in Real Hardware chapter

loads -> load

Massive mdbook update

updated instalation instructions for rusthello

fixed broken link to Enricos github

Fix "preparing the build" chapter linking back to a previous chapter as next step

Clear up the documentation for setting up and compiling

 - Update to latest mdbook
   - Switch to using book.toml
   - No empty links are allowed anymore. Comment out all empty links in
     SUMMARY.md
 - Add theme
   - Add favicon.png

Random updates

 - Update the asking questions page
 - Update the side projects page

Fix grammar in book.json.

Various updates and fixes

* Fix spelling: github -> GitHub, etc.
* Update the GitHub team list
* Move `null:` and `zero:` to the userspace schemes
* Change icons from Oxygen to Faba/Moka
* Remove statements that TFS is a ZFS implementation
* Add Intel HDA to the supported hardware
* Remove the `libredox` guideline
* Add some outgoing links where I think they're necessary

replace I with  we for consistency with rest of text

added cmake dependency

I didn't have cmake installed on arch, and my build failed. Thought it should be included in the book

Update outdated URLs

Since Bell Labs has died, the Plan9 project website only exists at a
mirror on 9p.io