have name for steps #12

:steps of Chord should be a keyword list [{name :: atom(), chord_step()}]

so that means user need to provide the name when using put_intervals drop_intervals update_voicing

the name user provide can be either binary or atom, but it will be converted to atom inside the functions

in build/1, when run_step returns {:error, msg}, the error message to include the name of the step that is run