Cleanup "master" terminology in the repository

[oleg-nenashev]

This project uses a lot of deprecated "master" terminology in documentation. It would be nice to clean it up, especially the README page and other user facing materials. All of that can be done in small atomic pull requests, contributors are welcome!

More info

• Inclusive Naming sub-project in Jenkins

[chiruu12]

Hey is this issue still open? would like to work on it if that's the case!