generate pybindgen/version.py in waf configure, closes #45

wscript

@@ -164,6 +164,10 @@ def configure(conf):
     conf.load('python')
     conf.check_python_version((2,3))
 
+    # this causes pybindgen/version.py to be generated by setuptools_scm
+    subprocess.run([conf.env["PYTHON"][0], "setup.py", "--help-commands"],
+                   stdout=subprocess.DEVNULL)
+
     try:
         conf.load('compiler_c')
         conf.load('compiler_cxx')