Fix false positive for NoUnused.Variables

Fixes a false positive for NoUnused.Variables: In the following code, the import of A would be reported even though it is used.

import A

a =
  let
    (A.Thing subValue) = value
  in
  subValue

Remove false positives for NoUnused.CustomTypeConstructorArgs

A fix for #25: Remove false positives for NoUnused.CustomTypeConstructorArgs

The rule now won't report the args of a custom type constructor that is found in a comparison:

-- Not reported
value == Foo 1
-- Still reported
value == fn (Foo 1)

Thanks @lydell for the suggestion 🙂

Resolving of false positives and false negatives

False positive fixes:

• NoUnused.Variables: Fixed a confusing situation where we import a custom type constructor and a type with the same name #29 (Thanks @kraklin, @sporto and @MartinSStewart)
• NoUnused.CustomTypeConstructorArgs: Never argument were being reported #31 (Thanks @SiriusStarr)
• NoUnused.Variables: Unused ports were being reported even when exposed with module A exposing (..) (Thanks @Augustin82)

False negative fixes:

• NoUnused.Patterns: Some unused patterns were not being reported when using nested case expressions (Thanks @Augustin82)

Detection of a lot of dead code

This releases includes a lot of changes, described in https://jfmengels.net/unused-patch-1-1-5/