enhanced readability of special characters protection when writing to pf

now there are 3 options for protecting special characters:
PfBackslashProtection, PfDoubleQuoteProtection, PfSimpleQuoteProtection

the default being PfDoubleQuoteProtection and the old one being
PfBackslashProtection

depending on this option, a string is quoted as in this example:
a\ string\ with\ \"special\"\ chars
"a string with "\""special "\"" chars"
'a string with "special" chars'

whereas a string without special chars won't be escaped or quoted
regardless the option (i.e. quotes are not added if there is nothing
worth quoting)