Unlocking efficient ppmpf folding macro expansion.

A series of changes in the <odreex/ppmpf/fold.hh> header allowing the macros
involved in folding operations to reach the maximum recursive macro expansion
by design, which is 10000 elements (ppmpf tuple / sequence "items"), in a much
more efficient manner than our previous implementation. Planning to allow a
user - defined upper limit within the [0 - 9999] range in eventual revisions
as a means to force particular limitations when applicable. The entire
construct is of course C99 ISO compliant, thus passes -pedantic checks on
all C++11 standard compliant preprocessors.