Accept keywords in keyword params (fix for #43)

[tomassedovic]

The first commit adds tests that expose the bug.
The second one is a fix.

[weavejester]

Thanks for the fix, but I'm going to solve this issue a little differently to your solution. I think that if the key is not a string, or cannot be converted into a keyword, then the key shouldn't be removed or altered. This prevents information being lost.