Issue 3777: Code improvements in satb.ly

Issue 3777: Code improvements in satb.ly

  Comment out the \version statement to ensure
  users still are warned if they omit their own
  \version statement

  Add prefix to macro and function names to avoid
  potential clashes with user names

  Return *unspecified* if macros are called with
  an undefined argument rather than #{#}

  Remove unnecessary use of "identity"

  Use "and" rather than "if" when false condition
  would return #f

  Convert tabs to spaces

  Use $ rather than # in \layout