Update documentation for Module#{private,public,protected,module_function}

Also, update NEWS for this change and the Kernel#load change.

NEWS.md

@@ -143,6 +143,13 @@ Outstanding ones only.
 
     * Integer.try_convert is added. [[Feature #15211]]
 
+* Kernel
+
+
+    * Kernel#load now accepts a module as the second argument,
+      and will load the file using the given module as the top
+      level module. [[Feature #6210]]
+
 * MatchData
 
     * MatchData#match is added [[Feature #18172]]
@@ -156,6 +163,12 @@ Outstanding ones only.
       modify the ancestor chain if the receiver has already prepended
       the argument. [[Bug #17423]]
 
+    * Module#private, #public, #protected, and #module_function will
+      now return their arguments.  If a single argument is given, it
+      is returned. If no arguments are given, nil is returned.  If
+      multiple arguments are given, they are returned as an array.
+      [[Feature #12495]]
+
 * Process
 
     * Process.\_fork is added. This is a core method for fork(2).
@@ -398,7 +411,9 @@ See [the repository](https://github.com/ruby/error_highlight) in detail.
   `$VERBOSE` is `nil`.  [[Feature #17798]]
 
 [Bug #4443]:      https://bugs.ruby-lang.org/issues/4443
+[Feature #6210]:  https://bugs.ruby-lang.org/issues/6210
 [Feature #12194]: https://bugs.ruby-lang.org/issues/12194
+[Feature #12495]: https://bugs.ruby-lang.org/issues/12495
 [Feature #14256]: https://bugs.ruby-lang.org/issues/14256
 [Feature #14394]: https://bugs.ruby-lang.org/issues/14394
 [Feature #14579]: https://bugs.ruby-lang.org/issues/14579

vm_method.c

@@ -2130,16 +2130,19 @@ set_visibility(int argc, const VALUE *argv, VALUE module, rb_method_visibility_t
 
 /*
  *  call-seq:
- *     public                 -> self
- *     public(symbol, ...)    -> self
- *     public(string, ...)    -> self
- *     public(array)          -> self
+ *     public                                -> nil
+ *     public(method_name)                   -> method_name
+ *     public(method_name, method_name, ...) -> array
+ *     public(array)                         -> array
  *
  *  With no arguments, sets the default visibility for subsequently
  *  defined methods to public. With arguments, sets the named methods to
  *  have public visibility.
  *  String arguments are converted to symbols.
  *  An Array of Symbols and/or Strings is also accepted.
+ *  If a single argument is passed, it is returned.
+ *  If no argument is passed, nil is returned.
+ *  If multiple arguments are passed, the arguments are returned as an array.
  */
 
 static VALUE
@@ -2150,16 +2153,19 @@ rb_mod_public(int argc, VALUE *argv, VALUE module)
 
 /*
  *  call-seq:
- *     protected                -> self
- *     protected(symbol, ...)   -> self
- *     protected(string, ...)   -> self
- *     protected(array)         -> self
+ *     protected                                -> nil
+ *     protected(method_name)                   -> method_name
+ *     protected(method_name, method_name, ...) -> array
+ *     protected(array)                         -> array
  *
  *  With no arguments, sets the default visibility for subsequently
  *  defined methods to protected. With arguments, sets the named methods
  *  to have protected visibility.
  *  String arguments are converted to symbols.
  *  An Array of Symbols and/or Strings is also accepted.
+ *  If a single argument is passed, it is returned.
+ *  If no argument is passed, nil is returned.
+ *  If multiple arguments are passed, the arguments are returned as an array.
  *
  *  If a method has protected visibility, it is callable only where
  *  <code>self</code> of the context is the same as the method.
@@ -2179,16 +2185,19 @@ rb_mod_protected(int argc, VALUE *argv, VALUE module)
 
 /*
  *  call-seq:
- *     private                 -> self
- *     private(symbol, ...)    -> self
- *     private(string, ...)    -> self
- *     private(array)          -> self
+ *     private                                -> nil
+ *     private(method_name)                   -> method_name
+ *     private(method_name, method_name, ...) -> array
+ *     private(array)                         -> array
  *
  *  With no arguments, sets the default visibility for subsequently
  *  defined methods to private. With arguments, sets the named methods
  *  to have private visibility.
  *  String arguments are converted to symbols.
  *  An Array of Symbols and/or Strings is also accepted.
+ *  If a single argument is passed, it is returned.
+ *  If no argument is passed, nil is returned.
+ *  If multiple arguments are passed, the arguments are returned as an array.
  *
  *     module Mod
  *       def a()  end
@@ -2423,8 +2432,9 @@ top_ruby2_keywords(int argc, VALUE *argv, VALUE module)
 
 /*
  *  call-seq:
- *     module_function(symbol, ...)    -> self
- *     module_function(string, ...)    -> self
+ *     module_function                                -> nil
+ *     module_function(method_name)                   -> method_name
+ *     module_function(method_name, method_name, ...) -> array
  *
  *  Creates module functions for the named methods. These functions may
  *  be called with the module as a receiver, and also become available
@@ -2434,6 +2444,9 @@ top_ruby2_keywords(int argc, VALUE *argv, VALUE module)
  *  used with no arguments, subsequently defined methods become module
  *  functions.
  *  String arguments are converted to symbols.
+ *  If a single argument is passed, it is returned.
+ *  If no argument is passed, nil is returned.
+ *  If multiple arguments are passed, the arguments are returned as an array.
  *
  *     module Mod
  *       def one