Crashes on Linux if no clipboard mechanism is installed.

[seapagan]

On Ubuntu at least, there is often no terminal clipboard handler (ie 'xclip') installed by default. In this case, trying to copy the Response will crash with a traceback and lose any work.

Output is a full taceback followed by:

PyperclipException:
    Pyperclip could not find a copy/paste mechanism for your system.
    For more information, please visit https://pyperclip.readthedocs.io/en/latest/index.html#not-implemented-error

I have opened a PR #98 that catches this cleanly