Separated finalizing a docset from installing it.

By finalizing, I mean delivering it to the install path. By installing it, I mean handing it to Xcode.

This distinction enables, for example, making an application that delivers a finished docset wherever the user wants it, as directed by a Save panel, without necessarily implicitly adding it to Xcode.
Merge in the addition of --finalize-docset, so that the application can use it.
Meaningless tool-enforced change: AppCode really wants these farther down in the project.
Use the new --finalize-docset flag to not implicitly load the docset into Xcode after generating it.

https://github.com/boredzo/appledoc/issues/10
Split up the destination URL across two flags so we don't save the docset inside of the docset the user wanted.

https://github.com/boredzo/appledoc/issues/8