Support overloaded method definitions

[backus]

Right now we just silently ignore them:

>> YARD::Registry.all(:method).select { |m| m.to_s =~ /percent_literal\?/ }.first.tags
=> [
  #<YARD::Tags::OverloadTag:0x007fc8d528a190 @tag_name="overload", @text=nil, @name=:percent_literal?, @types=nil, @signature="percent_literal?", @docstring="Check for any percent literal.", @parameters=[], @object=#<yardoc method RuboCop::AST::ArrayNode#percent_literal?>>,
  #<YARD::Tags::OverloadTag:0x007fc8d528a050 @tag_name="overload", @text=nil, @name=:percent_literal?, @types=nil, @signature="percent_literal?(type)", @docstring="Check for percent literaly of type `type`.", @parameters=[["type", nil]], @object=#<yardoc method RuboCop::AST::ArrayNode#percent_literal?>>,
  #<YARD::Tags::Tag:0x007fc8d5289dd0 @tag_name="return", @text="whether the array is enclosed in percent brackets", @name=nil, @types=["Boolean"], @object=#<yardoc method RuboCop::AST::ArrayNode#percent_literal?>>
]

see also #10