WIP support Buffer::Use

There may be cases where a user wants to use the original char* instead
of making a copy of the data. This adds support for the new Buffer::Use
method, while creating a shim for pre-v0.11.

Once a name has been approved I'll also add entries into the README.
Added NAN_CONSTRUCTOR method.
Documented NAN_CONSTRUCTOR() macro.
Added args
Fixed README
remove double-paren
I want to dispose Persistent<Object> as well as Persistent<Value>
Merge branch 'buffer-use' of git://github.com/trevnorris/nan into 0.2.0