Improve line matching and add better ins and del markers

Features:

• Highlighting: Support for matching "ins" and "del" markers to allow
  for a "change" marker
• Added similarity search feature to match similar lines for
  highlighting.

Fixes:

• Fixed a bug that prevented highlighting when more lines were deleted
  from a replacement block than added
• All lines are now split into prefix and content spans

Contributor:

• @escitalopram