fix setuptools scm usage - let pip handle it

pyproject.toml

@@ -0,0 +1,7 @@
+[build-system]
+requires = [
+    "setuptools",
+    "setuptools_scm[toml]"
+
+]
+build-backend = "setuptools.build_meta"

setup.py

@@ -7,7 +7,7 @@ def main():
         description='library with cross-python path, ini-parsing, io, code, log facilities',
         long_description=open('README.rst').read(),
         use_scm_version={"write_to": "py/_version.py"},
-        setup_requires=["setuptools_scm~=3.4"], # required due to legacy?
+        setup_requires=["setuptools_scm"],
         url='https://py.readthedocs.io/',
         license='MIT license',
         platforms=['unix', 'linux', 'osx', 'cygwin', 'win32'],