find unused and duplicate variables

[aioue]

Help stop variable sprawl by finding unused and duplicate variables.

[dellis23]

Sorry, just now saw your issues since github doesn't seem to want to notify me when new ones are created.

Anyway, I think I get the gist of your idea and think it's interesting, but could you flesh it out in a bit more detail what you think it would look like in practice? Maybe some simple examples would help.

[aioue]

in variables files, a foo: bar that isn't references anywhere else in the code is unused.

Dupes could come in two types

• foo: bar on two separate precedence levels means the least default-y one doesn't need to be there
• foo: bar and baz: bar could indicate accidental multiple variables for the same thing
  • similarly with baz: "{{ foo }}"