Add parallelization modules to Async category

[Grinnz]

Possible candidates: MCE, Parallel::ForkManager, IO::Async::Function (though redundant with IO::Async already there)

Ref: #10 #56

[PaulGWebster]

Should be restricted to things that can run on the three largest consumers of perl: BSD, Linux and Windows.

[karenetheridge]

fixed with #72.