Remove extra newlines in let bindings
Found while fixing #41 (closed), we put too much whitespace in lets.
For example, in the static formatting we currently print this:
foo = let x :: Int
x = 1
y = 3
in x
We should print this instead:
foo = let x :: Int
x = 1
y = 3
in x
We want to get rid of that extra newline between declarations.