Replace node classes with human types

[Jan Grodowski]

Current output of undercover includes class names, like:

🚨 5) node `parse` type: Imagen::Node::IMethod,
      loc: lib/undercover/options.rb:34:58,coverage: 69.23%

Replace type with a friendly text like "instance method", "class method" or "class". This involves adding a method to subclasses of Imagen::Node and displaying it in Undercover::Formatter

[Bartek Kruszczynski]

🙋‍♂️