Cleanup

[lue-bird]

Continuing #273 which had problems due to conflicts that I did not not know how to fix in the non-renamed remote branch of the PR.

All changes old + new:

• Introduce more general checks for sequence, join, repeatFlat and random checks
• Introduce MappableProperties
• Use "can be combined checks" more
• Organize helpers better into sections
• Introduce helpers to create type subset properties
• Fixed an issue where Random.map << always would be fixed to Random.constant
• Fixed an issue where List.any (\x -> x == (f x)) list would be fixed to List.member (f x) list
• Add documentation to checks with generic types

Can be merged.

[jfmengels]

Looks good so far (until https://github.com/jfmengels/elm-review-simplify/pull/277/commits/f5b54f3375e155d19eb340769722f7444262f7af) :+1:

[lue-bird]

Can be reviewed/merged. I won't add anything from now.

Edit: I guess that didn't happen even tho I tried... But the comment still stands!