Remove unused _separateElements()
More full-text indexing tweaks

Follow up from #440

- Convert curly single quotes to straight quotes before inserting
- Add General and Supplemental Unicode punctuation ranges to getClass()
  (so that fancy punctuation doesn't end up in words)
- Move single-quote test from getClass() to semanticSplitter(), and
  consider it a letter only if in the middle of a word
- Add comments to semanticSplitter()

This might be ever-so-slightly slower, but it's neglible. (War and Peace
seems to now take ~1570ms instead of ~1500ms for me.)