Solidity scanner taking documentation comments into account

A simple PR, where the scanner will conditionally not skip triple slash comments but instead scan them into comment literal tokens. Accompanying tests also created.

Next TODO step: Use this functionality in the parser.
@CJentzsch Looks like from previous code. isSorucePast_ is this class method and IsLine_ is in the namespace. Maybe better to namespace these static methods and keep lowercase letters than introduce different casing (::isLineTerminator maybe). /cc @chriseth