Enforce newline after assignment / clause.

This leads to more consistent formatting across entire Aiken programs.
  Before that commit, only long expressions would be formatted on a
  newline, causing non-consistent formatting and additional reading
  barrier when looking at source code.

  Programs also now take more vertical space, which is better for more
  friendly diffing in version control systems (especially git).

examples/acceptance_tests/050/lib/tests.ak

@@ -5,46 +5,55 @@ pub type Thing {
 }
 
 test let_1() {
-  let x: Data = 1
+  let x: Data =
+    1
 
   x == builtin.i_data(1)
 }
 
 test let_2() {
-  let x: Data = 1
+  let x: Data =
+    1
 
-  expect y: Int = x
+  expect y: Int =
+    x
 
   y == 1
 }
 
 test assert_1() {
-  expect thing: Thing = builtin.constr_data(0, [builtin.i_data(1)])
+  expect thing: Thing =
+    builtin.constr_data(0, [builtin.i_data(1)])
 
   thing.wow == 1
 }
 
 fn cast_to_thing(x: Data) -> Thing {
-  expect x: Thing = x
+  expect x: Thing =
+    x
 
   x
 }
 
 test assert_2() {
-  let thing = Thing { wow: 1 }
+  let thing =
+    Thing { wow: 1 }
 
-  let still_thing = cast_to_thing(thing)
+  let still_thing =
+    cast_to_thing(thing)
 
   still_thing.wow == 1
 }
 
 test tuple_1() {
-  let thing = (#"aa", #"bb", #"cc")
+  let thing =
+    (#"aa", #"bb", #"cc")
   thing.1st == #"aa"
 }
 
 test pair_1() {
-  let thing = (#"aa", #"bb")
+  let thing =
+    (#"aa", #"bb")
   thing.1st == #"aa"
 }
 // should not typecheck