Replaced `@name` with `@class_name` inside macros. And: instance vars inside macros don't have the `@` in their name anymore.

Explicit control of AST nodes inside macros. Must use "id" to get an id, and "stringify" to make a string literal with the node's string representation. No more implicit "id" call.

Added @instance_vars and @name inside macros. Removed hardcoded Struct#to_s and Struct#hash and implemented them with macros.

Added some more to macros: Array's join, map, select, any? and all?. And allow string interpolation inside macros.

More fun and power with macros: system, and some string methods (split, strip, downcase, upcase, lines)