Add infrastructure for reporting total allocated time in proposals.

This takes every [prop] item with mepi=y and approved=y and adds up the
awarded amount, grouping by the "facil" property. The awarded amount is in
either "award" (if that attribute is present) or "request". Each of these
should be formatted "<amount> <unit>", and each facility should have its
allocations recorded in consistent units.

The new TALLOCLIST command can then be used to list time allocations by
facility in alphabetical order. Each item has the attributes "facil", "total",
and "unit".
README.md: document the new features

The example still needs updating, though.