This PR fixes the SciPy 1.0 compatibility issues raised in issue #164. There are two main changes:

• Updated statesp.py and xferfcn.py to use the new forms of the scipy.signal library, for which the lti class no longer has accessors for num, den, etc. The fix is to directly call the ss2tf and tf2ss functions.

• Also had to add a check for scalars that are of a numpy data type, specifically for int64. Prior to Python 3, checking against int worked correctly, but this is no longer the case. As a fix, I added checks throughout the library against numpy.number, which captures all scalar data types in numpy.

I also checked (manually) to insure that this version works against scipy-0.19.0, which should mean it is OK for backward compatibility (this can be checked with PR #169 is merged).