Text tweaks covering most of the tutorial

[rzats]

Contains

Lots and lots of text tweaks that I worked on as I was going through the tutorial last week.

• Fixes all inline lists (these seem to require 2 spaces after the * in the comment, but most of them have 1 space and don't render correctly).
• Wraps all of the code in back-ticks.
• Ends most method comments with a ":" except the ones that aren't related to the method below it.
• Removes the markup that isn't properly handled by the parser: *italic*, *bold*, [Markdown links](), ####whatever the thing in TypeVariance.scala was. Replaces some of it with code blocks or other alternatives.
• Adds a few paragraphs to Ranges.scala that were stuck at the bottom of the file for some reason.
• Makes a few (opinionated) grammar tweaks. Feedback is welcome on these!

Also this closes #55.

[andrewnester]

wow, great 👍

[raulraja]

@rzats thanks so much!