Update "Development Status" in README to stable

[bact]

Currently the last section of README reads:

Development Status

Note: This library is currently unstable, and under development. Reviews, suggestions are welcome. Please enter an issue with any suggestions.

Since most of the Java libraries are just recently graduated to either 2.0.0 or 1.0.0,
should we update the READMEs as well?

We may replace the old "Development Status" section with:

Releases

All stable and pre-release packages are available in Releases.

Feedback and Contributions

Reviews and suggestions are welcome. Please submit an issue with any suggestions.

See CONTRIBUTING.md for contribution guidelines.

Please suggest how we should update the Development Status.