Tidy up boolean data type page

Hi all,

I wanted to clean up the boolean data type documentation page a bit,
so thought the following was needed:

- use a data type table like most of the other main data types so
it's more uniform (the the size of a boolean is only mentioned at the
very end and looks a bit odd, so removed that too)
- move the reference to the usage example to before the example
- minor text change in the first sentence so that it doesn't look
like it reads "boolean.boolean"

I've attached a patch with these changes, although feel free to list
the many reasons why this is a bad idea. ;)

Thanks

Thom