Finish workcache

[catamorphism]

See FIXMEs in std::workcache.

[msullivan]

Changing milestone to feature complete. Not really sure how important this is for that, though.

[emberian]

@catamorphism can this be closed / don't forget to close this when you're done with it (you are the one working on it AIUI)

[catamorphism]

The only item covered by this issue anymore is filling in the Logger struct. Frankly, I don't understand what the Logger code in workcache is supposed to do or why debug! messages aren't enough. If no one objects, I'll close this in a little while.