Pattern declarations should not be allowed at top-level.

[rupertlssmith]

This is not valid Elm syntax:

type Singleton
    = Singleton String

(Singleton val) = Singleton "test"

but this is:

val = 
    let
        (Singleton innerVal) = Singleton "test"
    in
       innerVal

[rupertlssmith]

The only pattern that should be allowed at top-level is varPattern.

Should remove patternDecl and replace it with valueDecl - which is like a funDecl but with no arguments.