Always indent with only 2 spaces except when function arguments span

multiple lines.

* indent with 2 spaces

```
Enum.map(list, fn outer ->
  Enum.map(outer, fn inner ->
    some()
    code()
  end)
end)
```

* exceptions

```
function(arg1, arg2,
         arg3)
```

Author: tonini

elixir-smie.el

@@ -240,7 +240,7 @@
       ((and (not (smie-rule-sibling-p))
             (smie-rule-hanging-p))
        (smie-rule-parent elixir-smie-indent-basic))))
-
+    
     (`(:before . "->")
      (cond
       ((smie-rule-hanging-p)
@@ -275,6 +275,12 @@
         (t
          (smie-rule-parent elixir-smie-indent-basic))))))
 
+    (`(:before . "fn")
+     (smie-rule-parent))
+
+    (`(:before . "end")
+     (smie-rule-parent))
+    
     ;; Closing paren on the other line
     (`(:before . "(")
      (smie-rule-parent))
@@ -284,7 +290,7 @@
       ((smie-rule-parent-p "after" "catch" "def" "defmodule" "defp" "do" "else"
                            "fn" "if" "rescue" "try" "unless")
        (smie-rule-parent elixir-smie-indent-basic))))
-
+    
     (`(:after . ";")
      (cond
       ((smie-rule-parent-p "if")

test/elixir-mode-indentation-test.el

@@ -572,24 +572,25 @@ x = do_something(
   :bar
 )")
 
-(elixir-def-indentation-test indent-inside-parens/2 ()
-  "
+(elixir-def-indentation-test indent-inside-parens/2
+    (:tags '(indentation))
+"
 x = do_something(:foo,
-                 :bar)"
-    "
+                    :bar)"
+"
 x = do_something(:foo,
                  :bar)")
 
 (elixir-def-indentation-test indent-inside-parens/3
-    (:expected-result :failed)
-  "
+			     (:tags '(indentation))
+"
 x = do_something(:foo, fn (arg) ->
                          do_another(arg)
                        end)"
 "
 x = do_something(:foo, fn (arg) ->
-                         do_another(arg)
-                       end)")
+  do_another(arg)
+end)")
 
 (elixir-def-indentation-test indent-lone-keyword ()
   "