Expose panic formatting in API

[kazcw]

Hi, I'm working on an Electron application, Enso. Enso needs to do multiple things in our panic hook: We have an application-specific API to submit the backtrace to, but we'd also like to display it with console.error. We want to minimize duplication of the functionality defined in console_error_panic_hook--especially the backtrace formatting, since it addresses browser subtleties.

This proposed change introduces a lower level function to the API, exposing the panic formatting functionality for use from another hook.

(Also, it increments the release version in Cargo.toml to match the currently-released version.)

[wdanilo]

@alexcrichton @fitzgen do you think it could be merged to this repo? We do not want to keep a local copy of it because it increases the maintenance burden :) I'm pinging you because other PRs are waiting really long time here, so I thought it might be helpful to let you know that this one is opened as well :)