Allow to configure font settings for preview

[estum]

This PR changes preview type to kUITypeHTML and adds keys to user defaults: fontFamily, fontSize, lineHeight. It solves issue #31

Configuration examples:

$ defaults write com.whomwah.quicklookstephen fontFamily "InputMono-Regular"
$ defaults write com.whomwah.quicklookstephen fontSize "13px"
$ defaults write com.whomwah.quicklookstephen lineHeight "21px"

[tsdorsey]

Thanks @estum. Will merge this soon.

[buggymcbugfix]

Any chance this will be merged soon? Cheers!

[tessus]

@estum your code compiles, but unfortunately the plugin stops working.

This is the error:

Error reading file at file:///path/to/file/README
The specified text encoding isn’t applicable.