* S\" ( [backslashed-strings_<">] -- str cnt )

scan the following text to create a literal just
like S" does, but backslashes can be used to
escape special chars. The rules for the backslashes
follow C literals, implemented techniques are
\n \r \b \a \f \v \e \777
and all non-alnum chars represent themselves, esp.
\" \' \ \? \! \% \( \) \[ \] \{ \} etcetera.
most importantly the doublequote itself can be escaped.
but be also informed that the usage of \' and \" is not
portable as some systems preferred to map [\'] into ["].
Here I use the experimental addition to map [\q] to ["] and [\i] to [']

FORTH/BASE zchar compiling primitive