skip extra var check
don't use Hash#merge (slow)
use converter directly when possible instead of calling #render
avoid extra #to_sym
assume we can use the same converter for the entire array by default
assume attrs are always passed as symbols
enable json compat mode
add ruby-prof
fixed typo
code generation implementation
use instance var directly
remove unused methods
use Hash as the base class to avoid extra object creation
collect parent attributes in one shot
call the object method directly
no need to return anything from collect_attributes