Increase module_function parity with public, private, and protected

[cupakromer]

module_function is not treated the same as public, private, or protected with at least the following cops:

• Style/AccessModifierIndentation
• Style/EmptyLinesAroundAccessModifier

Here is sample code which demo's this:

# .rubocop.yml
AccessModifierIndentation:
  EnforcedStyle: outdent

# lib/rubocop_test.rb
# A sample for rubocop
module  RubocopTest
  public
  def for_all_to_see
  end

  protected
  def for_the_kids
  end

  private
  def just_for_me
  end

  module_function
  def available_or_included
  end
end

$ bin/rubocop -v; bin/rubocop -D lib
0.25.0 (using Parser 2.2.0.pre.4, running on ruby 2.1.2 x86_64-darwin13.0)
Inspecting 1 file
C

Offenses:

lib/rubocop_test.rb:4:3: C: Style/AccessModifierIndentation: Outdent access modifiers like public.
  public
  ^^^^^^
lib/rubocop_test.rb:4:3: C: Style/EmptyLinesAroundAccessModifier: Keep a blank line before and after public.
  public
  ^^^^^^
lib/rubocop_test.rb:8:3: C: Style/AccessModifierIndentation: Outdent access modifiers like protected.
  protected
  ^^^^^^^^^
lib/rubocop_test.rb:8:3: C: Style/EmptyLinesAroundAccessModifier: Keep a blank line before and after protected.
  protected
  ^^^^^^^^^
lib/rubocop_test.rb:12:3: C: Style/AccessModifierIndentation: Outdent access modifiers like private.
  private
  ^^^^^^^
lib/rubocop_test.rb:12:3: C: Style/EmptyLinesAroundAccessModifier: Keep a blank line before and after private.
  private
  ^^^^^^^

1 file inspected, 6 offenses detected

This is semi-related to #730 which added some support for module_function in the Lint/DefEndAlignment cop.

[yujinakayama]

👍 for this.

@bbatsov @jonas054 Thoughts?

[bbatsov]

👍 from me as well.