Integration with oss-fuzz fuzzing service

Hi @hsivonen, I would like to help integrate this project into OSS-Fuzz.

• As an initial step for integration I have created this PR: https://github.com/google/oss-fuzz/pull/8652, it contains necessary logic from an OSS-Fuzz perspective to integrate encoding_rs.

• OSS-Fuzz is a free service run by Google that performs continuous fuzzing of important open source projects.

• As encoding_rs already have cargo-fuzz based fuzzing implemented, this makes it easily compatible with oss-fuzz out of box.

• If you would like to integrate, the only thing I need is a list of email(s), it must be associated with a google account like
  gmail (why?). by doing that, the provided email(s) will get access to the data produced by OSS-Fuzz, such as bug reports, coverage reports and more stats.

• As an alternative, if you don't have a google/gmail id, but still wish to integrate. I can add my mail id for time being and monitor bug/crashes.

• Notice the email(s) affiliated with the project will be public in the OSS-Fuzz repo, as they will be part of a configuration file.

Start by reviewing the OSS-Fuzz integration PR 8652 and the project's existing cargo-fuzz setup. The integration is done when OSS-Fuzz accepts the project configuration and the maintainer provides the required public Google-account email addresses.