Updated documentation to address ? and Option

[arienmalec]

I updated the documentation to address issue #1679. This is a semi-functional fix, I'm looking for feedback on:

1. If this documentation makes sense, fits the flow of The Book, and is the right tone and style
2. How to address cross referencing (I put a bunch of [REF] placeholders in there
3. Technical accuracy (I compiled all the code samples, but I'm not sure that I have all the technical details right -- particularly the discussion of ownership and moves as well as the details of the ? rewrite in an Option context.

[steveklabnik]

Hey there! I really really appreciate this PR! Unfortunately, we can't take really large changes like this. Thank you and sorry.

[dralley]

@steveklabnik would you consider keeping the wording and stripping down the examples (which are about 3/4 of the diff)?

[dralley]

@steveklabnik ^