Add breadcrumb list

[unasuke]

Motivation

When reading several modules has deeply nested namespaces like OpenSSL, the breadcrumb list is very useful.
In Japanese document (called rurema) has breadcrumb like this.

So, I introduce breadcrumb into rdoc.
I tested on ruby/rdoc and ruby/ruby.

ruby/rdoc

3f19b7a572b883291b7e8f66ec1726fd.mp4

ruby/ruby

26e76f9e48ba1567d606c2efa9001ee7.mp4

Changes

Add methods to RDoc::ClassModule to build breadcrumb metadata.

• RDoc::ClassModule#nesting_namespaces
  • returns array of namespaces that splitted full_name by ::
• RDoc::ClassModule#fully_qualified_nesting_namespaces
  • returns an array of fully qualified namespaces
  • To find RDoc::ClassModule instance from RDoc::Store#classes_hash and RDoc::Store#modules_hash

Add private methods to RDoc::Generator::Darkfish to build breadcrumb data for easy-to-use template erb.

• namespaces_to_class_modules
  • generate hash e.g. { "RDoc" => `RDoc::NormalModule` instance, "ClassModule" => `RDoc::NormalModule` instance }
• generate_namespaces_breadcrumb
  • generate array e.g. [{:name=>"RDoc", :path=>"../RDoc.html", :self=>false}, {:name=>"ClassModule", :path=>"../RDoc/ClassModule.html", :self=>true}]

Then, display the breadcrumb in the class template.

My concerns

• Should be displayed breadcrumb on top-level module/class?
• Should be escape class/module name?
• Should be made configurable to enable or disable breadcrumb?

[unasuke]

In Japanese document (called rurema) has breadcrumb like this.

To be precise, what is displayed in "rurema" is not a breadcrumb list but an inherited list of classes/modules. And this change don't provide an inherited list.

[nobu]

How about

Suggested change

	return namespaces if namespaces.length < 2
	@fqns ||= namespaces.map.with_index do |_, i|
	namespaces[0..i].join("::")
	end
	@fqns ||= namespaces.inject([]) do |list, n|
	list << (list.empty? ? n : "#{list.last}::#{n}")
	end

[unasuke]

Fixed at 0e05c99

[nobu]

I'm a little concerned about whether the plural term "namespaces" is appropriate here.

[unasuke]

@nobu Is it better for rename to namespace?

[nobu]

The word "namespaces" feels ambiguous; it doesn't represent that it contains what namespaces.
What about "nesting namespaces" or something?

[unasuke]

@nobu Renamed at 11d3c95

[st0012]

I love this feature 👍 Are you ok with rebasing the PR?