A sizable refactor

[michaelblyons]

Please test if you are so inclined!

This is mostly organization and restriction of scopes according to a distinguishing of expressions and a new statements context. All pre-existing tests pass, but there may be bugs that we didn't have tests for.

New

• True/False/Null get extended scopes
• Grouping of syntax rules within the file
• Embed C# in here-strings if a couple common patterns are detected
• Functions have full body scope
• Classes have full body scope
• Simple string format placeholders

Changed

• Many context names are pluralized, indicating that they will match multiple occurrences of their matches
• A new statements context restricts some contexts that were being nested everywhere. This is the most likely place to find bugs.
• Types have been sorted into builtin aliases (some may be missing) and formal types
• using imports can now only come at the top of the file, as the docs specify.
• Variables can now be named according to the insane official support.
• Strings can be quoted with curly quotes if you're a masochist.

Maybe

• DSC Configuration
• Better wildcard scoping
• More complex string format placeholders
• Context-aware flow controls
• Fully-recognized command expressions (i.e. no longer require Verb-Noun because we know it must be a command)

[michaelblyons]

@matteocoder Do you want to give this a try? Let me know if there are big regressions.