serialize: split float printing function declarations
serialize: split float printing function declarations

print_{float,double}s() and print_{float,double}() are now declared
separately. We will re-use the former for the integer flavours.

gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl,gopro/gopro-lib-node.gl