[Fix] issue 204 by removing trailing forward slashes in string selectors

[g5t]

One possible fix for #204 if any number of trailing forward slashes should not raise an error.

Fixes #204.

[SimonHeybrock]

Thanks, look reasonable. Do you feel like adding a unit test? If not, we can take care of that.

[MridulS]

The doc failure should be fixed by #207

[g5t]

I've added a unit test which will fail with a KeyError before my proposed fix.
It may be more-restrictive than necessary, since it only passes the assert if the same object is returned with and without a trailing forward slash in its path.

[SimonHeybrock]

Thanks!