move constant templates into their own files

which are textually included in the 'real' files

rather than making the files themselves templates.
add `setup.py constants`
typos in constant_names
Merge pull request #399 from minrk/constants

autogenerate files that involve constants

To add constants to pyzmq:

1. make appropriate changes to utils/constant_names.py
2. run `python setup.py contants`

No longer need to edit half a dozen files all over the place when a new constant is added, it should be just the one.
add constants from libzmq-3.3.0
updateconstants workaround for ZMQ_NULL
update constants
strip null-termination from bytes-sockopts

excluding IDENTITY
utf16 test fix
use numpy.isnan

to make sure no nan
update int sockopt test exclusions