Fix bad code generation
Rewritten Lace callback functionality. Now requires LACE_TYPEDEF_CB to define a callback type with arguments. Use TASK(...) to get a function pointer of the correct type. Use WRAP(...) to call callback functions from Lace tasks.
Get rid of DISPATCH architecture. Now requires LACE_ME in every non-Lace task that uses Lace.
Added benchmark pi (using monte-carlo)