Fix #53: improve dependency cycle error message

[frenchy64]

Closes #53

Error message for cyclic deps now pretty-prints all (unique) cycles in the dependency graph, from smallest to largest. I removed the :input map from the thrown exception, and replaced it with :cycles, the collection of cycles in the same order as printed in the error.

Example deps graph:

{:a #{:b},
 :b #{:c :a},
 :c #{:d},
 :d #{:a :b}}

Example (new) error message:

Execution error (ExceptionInfo) at lein-monolith.dependency/topological-sort (dependency.clj:249).
Dependency cycles detected!

+ :a
^ + :b
|_/

+ :b
^ + :c
|  + :d
|_/

+ :a
^ + :b
|  + :c
|   + :d
|__/

[greglook]

Thanks for tackling this! The new cycle representations look neat. I have some feedback on style/idioms in the code and a few opportunities to simplify things.

[greglook]

You should also merge master to pick up some new CI checks.

[frenchy64]

Merged master, tests pass.

[greglook]

Hmm, I wonder why CircleCI isn't running on your commits? 🤔

[drewinglis]

Hmm, I wonder why CircleCI isn't running on your commits? 🤔

It's supposed to:

Maybe @aengelberg would be willing to look in to this? :^)