tests/test-gendoc-sv.t

cext: extract revlog/index parsing code to own C file

parsers.c is ~3000 lines and ~2/3 of it is related to the revlog
index type.

We already have separate C source files for directory utilities
and manifest parsing. I think the quite unwieldy revlog/index
parsing code should be self-contained as well.

I performed the extraction as a file copy then removed content
from both sides in order to preserve file history and blame.

As part of this, I also had to move the hexdigit table and
function to a shared header since it is used by both parsers.c
and revlog.c

# no-check-commit

#require docutils gettext

  $ $TESTDIR/check-gendoc sv
  checking for parse errors