API call returns not conform specs

[stas]

Some calls do not return anything where they should return the result of _nn_check_positive_rtn.

A good example is the send() method.

This makes it hard to test.
Ideally we would have all the calls follow the nanomsg specs:
http://nanomsg.org/v0.5/nanomsg.7.html

Thanks for all the work so far!

[jb098]

Do you have any other examples of method calls that don't match the return specs of the C bindings?

[stas]

Sorry for the late response @jb098

I don't have to report any other potential issues. Thanks for reviewing this!