version number is too long for Windows paths

[daira]

​https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2739

As I wrote there:

I think we should simply release pycryptopp 0.7.2. The long version string is just not worth the hassle. Yes, Windows is broken, but neither Windows nor setuptools are going to get unbroken any time soon (and neither is Python 2.x going to get a workaround to convert to and from the "\\?\" long path prefix in all Win32 API calls that use paths, which would be the only practical alternative).