python 3.5 compatibility

[raziele]

Hi, I have encountered 2 issues when trying to use py-hackrf in python 3.5:

1. from core import hackrf returns an error "hackrf module can't be found'
2. import hackrf (from inside the core library) produces "syntax error" for line 29: print "".join(["/x%02x" % ord(c) for c in struct]) #

Working with python 2.7 works normally (at least for now)