Add the code that recodes URLs.

Add the code that recodes URLs.

This one function is an all-in-one:
 - UTF-8 encoder
 - UTF-8 decoder
 - percent encoder
 - percent decoder

The next step is add the ability to modify the behaviour, by telling
the function what else it must encode or decode and what it should
leave untouched.

Change-Id: I997eccfd2f9ad8487305670b18d6c806f4cf6717
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>