Structure describing a hunk of a diff.
A hunk
is a span of modified lines in a delta along with some stable
surrounding context. You can configure the amount of context and other
properties of how hunks are generated. Each hunk also comes with a
header that described where it starts and ends in both the old and new
versions in the delta.
Starting line number in old_file
Number of lines in old_file
Starting line number in new_file
Number of lines in new_file
Number of bytes in header text
Header text, NUL-byte terminated