Further Doc improvements

From @deltaidea on #254:

• @tjvr: Document save() / restore()
• Performance tips: avoiding ambiguity, using moo. (#81, #238, #243, #250)
• Debugging tips: inspecting that the right tokens are parsed, using nearley-test. (#253)
• Error handling:
  • List of possible exceptions. I imagine it’s short, but I’m not sure about it myself.
  • Empty parser.results. (#253)
• IDE support: syntax highlighting is supported at least in VS Code, probably in other editors too.
• Go through the source code and update references to the readme.
• @hardmath123: Introduction should also describe why people like nearley: it’s user-friendly, easy to get started, works on both the browser and node, etc.
• @hardmath123: I think “parse complex data structures” is not quite what we wanted to say, even in the original README. This is a good opportunity to find better wording. Complex languages, perhaps?

[tjvr]

@diegoperini You should absolutely be able to use save() and restore() with Moo.

[diegoperini]

It’s good enough. Thank you so much. Maybe after I get a grasp of it, I can write the docs for you as my thanks.