Merge pull request #31 from hintjens/master

Revert "Fix inability to close pipe in "expecting chunk" state"
Merge pull request #33 from hintjens/master

Implemented full protocol message filtering
Merge pull request #34 from hintjens/master

Basic clustering protocol implemented
Merge pull request #35 from hintjens/master

Finished up basic cluster test case
Merge pull request #40 from hintjens/master

Problem: after reader closes, WRITE asserts
Merge pull request #42 from hintjens/master

Problem: does not handle dropped writer properly
Fixed zpipes client to handle write errors

Fixes #43