repl: handle comments properly

As it is, the comments are not handled properly in REPL. So, if the
comments have `'` or `"`, then they are treated as incomplete string
literals and the error is thrown in REPL.

This patch refactors the existing logic and groups everything in a
class.

Fixes: https://github.com/nodejs/node/issues/3421
PR-URL: https://github.com/nodejs/node/pull/3515


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>