Releasing SymEngine

1. Update the AUTHORS page:

   bin/update_authors.sh

2. Change the version in https://github.com/symengine/symengine/blob/v0.3.0/CMakeLists.txt#L6 (If there's ABI breakage update minor version.)

3. Tag a v0.4.0 release on github:

   git checkout master
   git pull origin master
   git tag v0.4.0
   git push git@github.com:symengine/symengine master --tags

   • Finish the Release Notes at: https://github.com/symengine/symengine/wiki/Release-Notes-0.4

   • Add there the list of authors who contributed to this release:

     bin/release_authors.sh v0.3.0 v0.4.0

   • Go to https://github.com/symengine/symengine/releases/tag/v0.4.0, click "Edit tag" and copy & paste the Relese Notes from the wiki

4. Download the source archive from github and upload the archive as a release artifact.

5. Update symengine.py and SymEngine.jl and make sure existing tests don't break.

   • Update symengine_version.txt in symengine.py and make sure tests don't break

   • Change the version in https://github.com/symengine/SymEngineBuilder/blob/v0.3.0-3/build_tarballs.jl#L7 and tag a new version (v0.4.0-0). (This builds Linux/glibc, Linux/musl, OSX, Windows, FreeBSD binaries for x86_64, i686 and also aarch64, ppc64le)

   • Update https://github.com/symengine/SymEngine.jl/blob/master/deps/build.jl

6. If no regressions, tag the release on github and do 3.