node.js: Added `toJSON()` and `INSPECT_MAX_BYTES` to NodeBuffer interface

See issue: https://github.com/borisyankov/DefinitelyTyped/issues/2147
See docs: http://nodejs.org/api/buffer.html

`toJSON()` and `INSPECT_MAX_BYTES` have been missing in the v.0.10 node.js definitions.

Added to the `NodeBuffer` interface for now, although it is marked as 'deprecated', as the interface `Buffer` extends `NodeBuffer`.