Teach commit parser about author/committer email + timestamp

We want all four of these when showing a commit, so save them in the
commitinfo struct.

Btw: There's probably no good reason to save committer timestamp since
it's already available in commit->date. But it doesn't hurt us either,
and it makes the parser look more complete, so we just do it.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>