#4 Add support of python 3.7

[Dmitry Demidov]

With python 3.4 it is ok. With 3.6 and 3.7 the compilation process with cython (both on gcc and msvc) gives error:

src\pyclp\pyclp.pyx:753:40: Cannot convert Python object to 'pword'

Here it is:
if len(tail) == 0:
tail_pword=pyclp.ec_nil()
else:
tail_pword=PList(tail)

I manually fixed it to:
if len(tail) == 0:
tail_pword=pyclp.ec_nil()
else:
tail_pword=PList(tail).get_pword()

But for this reason I couldn't install pyClp automatically in PyCharm.