buffer: add includes() for parity with TypedArray

Add Buffer#includes() by wrapping an indexOf and performing a strict
equals check to -1.

The includes method takes the search value, byteOffset, and encoding as
arguments.

The test is a modified version of the indexOf test.

Fixes: https://github.com/nodejs/node/issues/3552
PR-URL: https://github.com/nodejs/node/pull/3567


Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>