Make StdOut buffer size configurable

[qingqu]

Default buffer size used by bufio.Scanner is 64kb, it will not work if the output is bigger than 64kb, this change makes the StdOut buffer size configurable so that the client code can choose to user default buffer or user defined buffer size.

I confirm that this contribution is made under the terms of the license found in the root directory of this repository's source tree and that I have the authority necessary to make this contribution on behalf of its copyright owner.