urls should not be downcased

[maia]

While it's rare that a URL uses uppercase letters, some do. And as urls are case-sensitive, they should not be transformed when using the option downcase: true, so the following is not desired:

> PragmaticTokenizer::Tokenizer.new(downcase: true).tokenize("http://test.com/UPPERCASE")
=> ["http://test.com/uppercase"]

[diasks2]

I added a spec for this (f2198d6). This is a tough one. I can't think of a good way to do it without taking a big performance hit. If you have any ideas let me know.