Remove unused package dependencies
Support the ParFuture class from the abstract-par package

The monad-par-extras package has a bunch of handy combinators built on this
class which can immediately be used with Hurtle, such as parallel map,
map-reduce, etc.
Use monad-resumption package rather than pipes

monad-resumption is really simple and easy to understand, pipes is... less so.
Get rid of dependency on free package, just use a custom free monad
No further need for the TypedStore2 module

If we pass the SomeRequest values through the SentRequests then there's no need
for a lookup after the SentRequest resumes.  Simpler, less to go wrong, hurrah!
'fork' and 'request' don't need Connection in their contexts
Merge branch 'simplify'