Support for defn about cljfmt HOT 1 OPEN

This might be better split into two issues.

The first, removing parentheses around functions with one arity, seems pretty specific to functions alone. We could add that in as its own rule, and it would likely only be a few lines of code.

The second issue, fixing newlines, seems a more general issue, like indentation. I've been thinking about specifying rules to denote valid points for newlines. For instance:

;; valid
(if x y z)

;; valid
(if x
  y
  z)

;; invalid
(if x y
  z)

I'm not decided on the syntax for specifying the rules yet. Perhaps something like:

[[if _ _ _]
 [if _ \n _ \n _]]

For when and similar, we also need to have some repetition:

[[when _ _ *]
 [when _ \n (_ \n) *]]

And for defn, some sort of predicate/type match:

[[defn _ :vector \n (_ \n) *]
 [defn _ \n :string \n (_ \n) *]]

from cljfmt.