Introduce a SPLIT_BEFORE_ENDING_BRACKET knob

This controls whether closing brackets get a separate line in multiline
literals.

The default is enabled:

    foo = {
        'a': 1
    }

However it can now be disabled:

    foo = {
        'a': 1}
diff --git a/README.rst b/README.rst
index 21d0692..86ab6c6 100644
--- a/README.rst
+++ b/README.rst
@@ -439,6 +439,10 @@
     Set to ``True`` to prefer splitting before ``&``, ``|`` or ``^`` rather
     than after.
 
+``SPLIT_BEFORE_CLOSING_BRACKET``
+    Split before the closing bracket if a list or dict literal doesn't fit on
+    a single line.
+
 ``SPLIT_BEFORE_DICT_SET_GENERATOR``
     Split before a dictionary or set generator (comp_for). For example, note
     the split before the ``for``: