Use NS_ENUM and NS_OPTIONS for the log level and log flags

You can just pick fd9d3ed if you only want the enums/options.
This change does make CocoaLumberjack more Swift-friendly, but more work will be needed to make it viable.
The variables are actually defined in the Xcode project, with Xcode generating a C Source file with the variables.

No, they aren’t needed and can be safely removed. 
> On Sep 28, 2014, at 7:51 PM, Ernesto Rivera <notifications@github.com> wrote:
> We could keep it inside #ifndef COCOAPODS and update the Info.plist, as I guess that is what this looks up.
> 
> —
> Reply to this email directly or view it on GitHub <https://github.com/CocoaLumberjack/CocoaLumberjack/pull/338/files#r18134910>.
>