[anyword-hint addon] Add
Add registerHelper/getHelper mechanism

Move hinting functions into it.
[fold addon] Move to registerHelper
[lint addon] Move over to registerHelper
[manual] Fix missing </code> tag
[matchtags addon] Fix inefficiency

Issue #1653
[foldgutter addon] Add
Rename combineRangeFinders to CodeMirror.fold.combine
[match-highlighter addon] Improve showToken option