Add ability to be able to limit output by number of characters

[lenchantin]

I'd like to be able to limit the output to a specific number of characters while retaining JSON or HTML. For instance, I'd like to be able to limit the characters output to 50 without risking cutting off an HTML end tag if it cuts in the middle of a word. Maybe something like $output->getHTML()->limit(50, '...') - with the first value being number of characters, and second being what you'd append to the end of the string should it cut off any characters.