Fixed some minor warnings in the compiler, and linked in the math library

quad/computation_graph/Makefile

quad/computation_graph/src/main.c

quad/computation_graph/src/node_accumulator.c

quad/computation_graph/src/node_accumulator.h

quad/computation_graph/src/node_add.h

quad/computation_graph/src/node_constant.h

quad/computation_graph/src/node_gain.h

quad/computation_graph/src/node_mult.c

quad/computation_graph/src/node_mult.h

quad/computation_graph/src/node_pow.h