Issue 829 - configuration regex options are not being parsed as RegExp instances

[bbabic]

As discussed in Issue 829 configuration file options which holds regex values were not treated as RegExp instances.
This is just a quick-fix for mangle options, proper fix needs to be able to handle any regex option.

[fabiosantoscode]

Hey there :)

I had a look around, and it seems like only three options are missing:

• keep_fnames and keep_classnames compress options
• unsafe_methods compress options

Compress options are treated in the Compressor constructor in lib/compress

I would really appreciate it if you also formatted those options to make this PR more complete.

Thanks in advance :)