python 3.5 compatibility

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)