lei q: use git approxidate with d:, dt: and rt: ranges
Instead of having --(sent|received)-(before|after)=s
command-line switches, we'll just try to make sense of argv so
it's usable within parenthesized statements and such.
Given the negligible performance penalty with Inline::C
process spawning, we'll probably wire this up to the
WWW interface, too.
"d:" is for mairix compatibility. I don't know if "dt:" and
"rt:" will be too useful, but they exist because of IMAP
(and JMAP).