parser: Extend series heuristics to include other metadata

parser: Extend series heuristics to include other metadata

Not every series will include the reference headers necessary to do
proper series-ification, particularly those generated without the help
of 'git-send-email' or similar.

Make life a little easier for these folks by attempting to match on
other heuristics of the series: submitter, version, number of patches,
project (mailing list) and date. The last of these is particularly
important to prevent duplicate series getting munged together.

Signed-off-by: Stephen Finucane <stephen@that.guru>