FIX: Support for IMG URLs with parentheses in them.

Currently markdown-js doesn't support image URLs with parentheses in them. Having parentheses in URLs is valid and some sites like Wikipedia use them often.

This fix will first attempt to use a strong regexp to match URLs more accurately including parentheses. If it fails, it will revert to the old regex which is more permissive. 

There's a new test for a funky URL which now passes (and all previous tests pass too.)