o Reworked changing and setting of traps associated with outputting
left and right margin notes. See BUGS.
o Bracketed outputting of margin notes diversions with .nf/.fi.
o Corrected docs MN_INIT so that the optional first arg is properly
given as RAGGED | SYMMETRIC
o Fixed MN_INIT macro routine that reads MN_INIT args into strings
so that the strings are first "initialized" with the @ character
if the corresponding arg is blank. Since MN-init tests for \A
and \B (correctly, I hope) for each of its args, the @ character
should be safe.