Support building wheels (PEP-427)

Universal is used to identify pure-Python module(by bdist_wheel). For
these, it is sufficient to build a wheel with _any_ Python ABI version
and publish that to PyPI (by whatever means).

Change-Id: Ib15e61ce3edf6f2694795167c85d40457bf11292
diff --git a/setup.cfg b/setup.cfg
index 23a97ff..79f538f 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -21,3 +21,6 @@
 all_files = 1
 build-dir = doc/build
 source-dir = doc/source
+
+[wheel]
+universal = 1