Added PPMPF_UTUP_FOLDL, PPMPF_UTUP_FOLDR

These will substitute current PPMPF_TUP_FOLDL, PPMPF_TUP_FOLDR high order
macros after transition to the new construct is done. The _TUP_ token in the
identifiers involved, will signify "safe" tuples, aka parenthesis enclosed
comma separated tokens in a parenthesis enclosed series.
Added PPMPF_UTUP_FOLDL_OF for unsafe tuple folding.

This will eventually take over the current PPMPF_TUP_FOLDL_OF implementation,
which itself will be converted into safe tuple mode. Still in transition!
Introduced ppmpf safe tuple constructor, resolved #8

This is the ppmpf safe tuple constructor, the following rules are valid:

    1) PPMPF_TUPLE()      -> ()
    2) PPMPF_TUPLE(1)     -> ((1))
    3) PPMPF_TUPLE(1,2)   -> ((1),(2))
    4) PPMPF_TUPLE(1,[],) -> ((1),([]))

Notice that if the last element used is a token with special characters, the
trailing comma is used as an escape character. Special characters are all
those that if concatenated with a random character, they result in at least
one invalid token. Tests have been added as well.