setup.py fails on windows du to no icu-config binary

Created by: amynbe

The following line:

ICU_VERSION = subprocess.check_output(('icu-config', '--version')).strip()

( https://github.com/ovalhub/pyicu/commit/81830b36d85c12bcab959dce4d9f4332cb9ec6bc#diff-2eeaed663bd0d25b7e608891384b7298R11 )

Fails on windows for which an icu-config exe doesn't exist (the icu win binaries include a bunch of dll and exe files but no icu-config).