Set the `catch_exceptions` value for the whole runner

[azmeuk]

I always pass catch_exceptions=False for all my test suites.
It would be convenient to configure this value once for all in CLIRunner for example.

For example, we could add a CLIRunner.catch_exceptions parameter, and make invoke use that value if not directly passed in parameter of invoke. Then I would just have to put the runner in a pytest fixture and that would do the thing for me.

If that is OK, I can open a PR for this.

What do you think?

[Rowlando13]

Look like catch_exceptions=True is the default option, so you should not need to pass it in.

[azmeuk]

My bad, I meant the other way. I edit the OP.

[davidism]

Might make more sense to add the param to __init__, and default to None in invoke. If it's None, it will use whatever was set in __init__.