Updates for Batteries 2.0.0

* Add some functions removed from Batteries pervasives to ppatteries
* Filter updates
* Move to Map.PMap

See
https://github.com/ocaml-batteries-team/batteries-included/wiki/Interfacechanges12
Replace first,second with Tuple.Tuple1.map{1,2}
Fixes for tests

All pass
Update requirements

All tests pass
Replace |- with %> where possible

Also restore the old version of pull_each_out
MCL bump
Merge pull request #303 from matsen/303-batteries-2.0

Move to Batteries 2.0. Thank you @cmccoy!