Improve consistency, efficiency

Aux color-related constants begin at 1 (e.g. CURSED_AUX1) instead of 0
for consistency with the numbering of the color_aux* options.  bkgdset()
is used instead of attron() for consistency with the rest of the code.

Also, dump_print_buffer() is split into dump_print_buffer() and
dump_print_buffer_formatted() for efficiency.  The former does not check
for escape codes and so can avoid an extra pass over the buffer.
Document color formatting in man page

Auxiliary color options and the format specifiers for coloring are
documented in the cmus man page.