update and expand URL scheme resource example

Created by: GlenDC

The most important reason for the work done in this pull request was to make sure the example code in this book chapter is up to date with the latest production code.

Besides this I wanted to clarify how to run the example, as that was not clear to me as a beginner. Beyond that I also wanted to add some extra exercises to give the reader more confidence before he/she would start writing a scheme from scratch.

@jackpot51 could you perhaps amend to this commit or explain me how to than actually test it. For now I can compile & run this example on Redox (via qemu), but I have no idea how to actually interact with it, could perhaps give some fun examples, so we can add some simple ways to interact with the example running. Might give also inspiration to the reader on how to test his/her own (brainfuck) scheme.