Extend pylint to have an Exercism Plugin and Exercise-specific Checkers

[yawpitch]

Never tried it, but Pylint is pretty pluggable and it looks like extending it will be much more flexible than chasing through the raw ast representation.

https://breadcrumbscollector.tech/writing-custom-checkers-for-pylint/

Also should let us get two birds with one stone.

[BethanyG]

See #26 as an intermediary step.