Fixup IntelliSense-related behavior

[mark-wiemer]

Closes #110.

Hoping to address #250

Breaking changes:

• Rename some settings. Users will have to manually adjust these new settings from the defaults to match their old settings:
  • ahk++.formatter.indentCodeAfterSharpDirective is now ahk++.formatter.indentCodeAfterIfDirective
  • ahk++.language.enableIntellisense is now ahk++.intellisense.enableIntellisense
  • ahk++.file.maximumParseLength is now ahk++.intellisense.maximumParseLength

Other changes:

• IntelliSense no longer suggests words when a user presses space (Issue #110)
• IntelliSense now suggests foo(p1, p2) instead of foo (p1,p2)
• Improved descriptions of settings

Engineering changes:

• prefer-const
• Add manual tests to repo (previously were untracked)
• Update v1 and v2 demos
• Method class now refers to uriString: string, not document: vscode.TextDocument
• Rewrite CompletionProvider.provideCompletionItems and add unit tests