Release to pypi procedure

We follow release naming convention similar to tensorflow:

Releases come from release branches named rx.y, for example r0.4. Multiple release maybe come from the same release branch. When we release to pypi we tag the commit the release is on with vx.y.z, for example v0.4.1.

The steps to release to pypi:

1. take a branch, for example git checkout -b r0.4
2. edit/commit the file VERSION to include the full version number (x.y.z), for example 0.4.1
3. tag the release commit with vx.y.z, for example v0.4.1
4. push the branch to github, wait for CI to bless the build
5. build the wheel: python setup.py bdist_wheel
6. call twine upload dist/tf2onnx-*.whl

If you want another release from the same release branch (ie. you release a patch), merge your changes and go to step 2. If you started a new branch you want to increment the version in VERSION.