Strip comments from compiled PHP (artisan optimize)

The argument added strips out all of the comments, reducing the size of the compiled PHP file to half.

This should likely improve performance (if only a little) but I haven't tested it. 

It might also be worthwhile to run the generated file through "php -w" to strip whitespace as well.

This pull request brings the size down from 650 to 350kb. The php -w command brings that down to 270kb.