Permit attributes on parameters

[fmease]

Motivation

• ~documentation comments for record fields~ (depends on the design of records, #18, #109)
• enables finer-grained lint level controls
• @lazy (but this will probably be replaced with a Lazy type like in Idris 1)

Examples:

data Person: Type of
    person
        ;; some documentation
        (name: Text)
        ;; some other documentation
        (age: Nat): Person

data Dummy
    @alpha @(beta) (A: Type)
    @gamma (@delta B: Type): Type of

Specification

Parameter attributes are stored inside of pi type literals.

Unresolved questions

• Should attributes be allowed inside of parameter parentheses or only outside?
• Does this remain relevant at all if we go for #109?