Use # to introduce comments

[JukkaL]

Perhaps it would be better to use # to introduce comments instead of the current "--". Hash is simply more popular -- Python, Ruby and shell scripts all use it. Since we already support an initial #! comment, this would remove a special case from the lexical syntax. Additionally, the language would be more "Python-like".

During migration both -- and # would be supported. Eventually, before 1.0 release, remove support for "--".