*Backfills hunk_generator with extra newline to account for 'true'
trailing newlines that should be included in diff calculation.
  Example:

  "cat\n".split("\n") => []
  "cat\n\n".split("\n") => ["cat"]

  "cat\n".split("\n", -1) => ["cat", ""]
  "cat\n\n".split("\n", -1) => ["cat", "", ""]

*Removes extra newline representation from hunk_generator when crafting differ
output message.

diff calculation