Add name: &str argument to Tool::new()

Hello,

I am writing a highly specialized test-runner for an internal application. It was desirable to have the test output reports in the ctrf format and I found your ctrf-rs crate to be useful.

In this little merge request I introduce (name: &str) as a new argument to the Tool::new() function, so that the test reports can show the correct name of the testing tool being used.