Update usage of code-blocks in haddock syntax.

This allows us to hyperlink to identifiers inside code blocks with
haddock, much like the lens package does.

This also makes some small tweaks to the examples.

Signed-off-by: Austin Seipp <mad.one@gmail.com>
Make Printf example slightly less verbose.

Signed-off-by: Austin Seipp <mad.one@gmail.com>