Added `toJSON()` and `INSPECT_MAX_BYTES` to NodeBuffer interface

See docs: http://nodejs.org/api/buffer.html#buffer_buffer_inspect_max_bytes

Added to the NodeBuffer interface for now (marked as deprecated), as the interface Buffer extends NodeBuffer
Merge pull request #2154 from johnnycrab/master

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