Exclude packages

[fredrikaverpil]

Why is the change needed?

• An --ignores argument? #130

What was done in this PR?

• Added the --exclude-deps argument.
• Refactorings.

Are there any concerns, side-effects, additional notes?

• I've been mixing terminologies... the README.md mentions dependencies and packages interchangeably. Should probably settle on one of them and keep things consistent. This also applies to the source code. Doesn't need to part of this PR although it could affect the argument name;
  • --exclude-packages
  • --exclude-dependencies
  • --exclude-deps

Checklist, when applicable

• Added test(s)
• Updated README.md
• Is this a backwards-compatibility breaking change? (No)
• Resolves: An --ignores argument? #130

[fredrikaverpil]

I'm considering renaming everything in the source code from package and dependency into dep. This also means keeping --deps-file and here introducing --excluded-deps. The README will be updated to only mention "dependencies" and not "packages". I'll sleep on this now.