Allow to parse a single project - no comparison

**Is your feature request related to a problem? Please describe.**

I often want to quickly find out "what are the dependencies of this project" or "what are the build settings of this project". However, opening Xcode and navigating the UI can be slow and cumbersome. `xcdiff` might provide a quick way to get at this info.

**Describe the solution you'd like**

It might be nice if you could invoke `xcdiff` to just parse and print these values without any comparison against another project

Start by tracing xcdiff’s existing project-comparison command and how it parses an xcodeproj. Define the single-project invocation around the requested dependencies and build settings, then verify that it prints those values without requiring a second project.

Written by the indexing model from the issue text.