redundant parens in a few places

[bobzhang]

Here is a non-complete list where I think parens are redundant (work in progress). Note I am not suggesting to remove all of them, but to suggest to remove some of them to take advantage of hand written parser

• [ ] first class module module (X) vs module X module ({ ...}) vs module {..}
• [ ] inline records in types

type t = 
  | A ({ x : t })

• [ ] inline records in pattern match
• [ ] inline records in expressions
• [ ] wild card patterns A (_) vs A _