Refactor initial chunking to be line‐based

Refactor initial chunking to be line‐based

The old parsing mechanism operated primarily on large string chunks,
  which were re‐parsed into lines potentially multiple times.
This refactor changes the parsing to use lines and ranges, which is a
  little more verbose/complicated from an X·Path perspective (it
  requires a lot of `generate-id()´ comparisons) but hopefully, on the
  whole, better.