doc: call console module 'console' not 'stdio'

The console module has always been called 'stdio' in the
table-of-contents, but nowhere else, since its name is
'console'. This makes it difficult to find.
src: clean up `using` directives

Remove the unused ones and alphabetically sort the ones that remain.
stream_wrap: remove bogus assert

Libuv may provide a NULL buffer to the uv_read callback in case of an
error, so with this assert we'd be using the api incorrectly. None of
the current DoRead implementations rely on this constraint, either.
doc: cleanup addons docs for 80 char lines
doc: cleanup addons code, fix isolate positioning

isolate declaration global and above `using namespace v8`
removed BUILDING_NODE_EXTENSION and tidied up code