Update sp.py

Multifile preprocessing now possible:

//
// source1.ppc:
<<<declare some integers>>>
a = b = c = 7;
<<<do something amazing>>>

*** declare some integers ***
    int a, b, c;
    <<< declare special >>>
!!!
*** do something amazing ***
    superfunctionyay(a, b, c);
!!!

//
// source2.ppc:
*** declare special ***
    int spec;
!!!

//
// dest.c:
int a, b, c;
int spec;
a = b = c = 7;
superfunctionyay(a, b, c);