specify output/compress options inline

[eleith]

with tools like jshint, it has been valuable to have global options be configured by our build tool, but then on certain files that need to be treated differently, to specify turning on/off certain options inline in the js file through comments like

/* jshint undef: true, unused: true */

it would be nice to do that with uglifyjs2. for example, one of our files we want to preserve quotes around object keys with the quote-keys output option, but we wouldn't want that to be turned on for our other files.

we can hack around it manually, but the inline option would be cleaner.

[avdg]

This issue is related to #361

[rvanvelzen]

We'll track this in #361. Thanks!