fix raspberry pi arch ZMQError: Address family not supported by protocol
Merge pull request #596 from y12studio/raspberry-pi-arch-fix

fix raspberry pi arch ZMQError: Address family not supported by protocol
Test API of pybitcointools.

* Only test the part of API that is currently used.
Switch from arithmetic to pybicointools.main.
Drop unused code, together with import.
Drop arithmetic tests.
Drop arithmetic module.