Update sp.py

Expanded error-checking.
Got rid of idea of "<<<MAIN>>>".

Added uniqueness option for definitions.

WHAT IT DID:
//source.ppc:
***! hey***
 int a;
!!!

***bay***
 <<<hey>>>
 bay(a);
!!!
***yay***
 <<<hey>>>
 yay(a);
!!!

<<<bay>>>
<<<yay>>>

//dest.c:
int a;
 bay(a);

 yay(a);