Adding graphviz support in dump

[jeffctown]

Hey there! 👋

Motivation

I came here looking for the same thing mentioned in #646: a way to output a dependency graph from xcodegen project files

Whats in this PR

I added support, like specified in the linked issue.

The following will output a Graphviz to stdout:

xcodegen dump --type graphviz

And this will output to a file:

xcodegen dump --type graphviz --file ~/Desktop/output.viz

When the output is pasted into an online graphviz tool it can produce a target dependency graph based on xcodegen project files.

This was created from the Test Fixture project in Tests/Fixtures/TestProject/:

What Should We Discuss?

Well, I'm adding a dependency on a graphviz package. It is actively maintained.

Is this worth adding a dependency? 🤷‍♂️

[yonaskolb]

This is fantastic @jeffctown, thank you! 🎉 I'm not too familiar with graphviz, are there any attributes or settings you would suggest for showing what sort of dependency a node is? (carthage, target..ect)

[jeffctown]

@yonaskolb - What a great question! This got me thinking, and I decided to update the style to be as close to a UML dependency diagram as possible. My hope is that by using a standard, the diagrams will be understandable by the broadest audience.

Changes Since Last Review:

1. Updated all Nodes' shape to be a box.
2. Updated Edges to use dashed lines since they are dependencies.
3. Updated dependency labels to include <<external>> for any dependency targets who's type is not .target (external to the project).
4. I also added a CHANGELOG entry, and updated the README.

Updated TestProject Diagram:

[yonaskolb]

How about including the name of the dependency type instead of external? Same as enum cases but strings

[carthage]
Alamofire

[jeffctown]

Updated here, with a few tests.

[yonaskolb]

Love it! Thanks again @jeffctown! I think this will be really useful for many people