Automate the release process

[wixette]

With the commit 87154f3, A new SeedLang release can be manually published to NuGet. It's good enough for the current dev stage.

Going forward, we will need to automate the release process, for example:

• Once a new version number is given with a release PR, and the PR has been approved by the core team:
  • Auto build and verify the source code.
  • Auto create the release branch and add the git tag.
  • Auto publish to NuGet.
  • Auto add release info and links on the git releases page.
  • ...