Since the function in question is the only one on the call stack above
the reset method, there's no need to invoke the captured continuation
-- we get the same effect by just returning normally, and it's more
efficient that way.
Turns out Function can do the jobs of both CallbackReceiver and
FunctionReceiver, so I've removed the latter two.
Also, shift and reset should work with a combination of types, not
just a single type, so I've expanded their generic signatures.
I've been told by knowledgeable people that it is impossible to
implement composable continuations (AKA delimited continuations AKA
shift/reset) in terms of call-with-current-continuation. Since I
don't yet understand why that is, I figured it would help my
understanding to attempt it and see how it fails.
Previously, I used a shell script to extract modification date ranges
from the Git history, but that was complicated and unreliable, so now
every file just gets the same year range in its copyright header. If
someone needs to know when a specific file was modified and by whom,
they can look at the Git history themselves; no need to include it
redundantly in the header.
