RCR 350: Make Kernel#caller return Array of Structs

Currently, Kernel#caller returns Array of Strings.

That means, when you want just a name of the method, you need parsing:

 def parse_caller(caller_output)
   if /^(.+?):(\d+)(?::in `(.*)')?/ =~ caller_output
     {:file => $1, :line => $2.to_i, :method => $3}
   end
 end
 parse_caller(caller.first)[:method]

That's sometimes a pain.

 class CallerInfo < Struct.new(:file, :line, :method)
   def to_s
     "#{file}:#{line}:in `#{method}'"
   end
 end

The code above could be simpler:

 caller.first.method

 module Kernel
   CallerInfo = Struct.new(:file, :line, :method)
   class CallerInfo
     def to_s
       "#{file}:#{line}:in `#{method}'"
     end
   end
   alias unstructured_caller caller
   def caller(level=1)
     if level < 0
       raise ArgumentError, "negative level (#{level})"
     end
     unstructured_caller(level+1).collect do |item|
       /^(.+?):(\d+)(?::in `(.*)')?/.match(item)
       CallerInfo.new($1, $2.to_i, $3)
     end
   end
   module_function :caller
 end

CallerInfo#to_s is imcomplete.