move PD_FLOATSIZE message from Pd Window to "About Pd" using [pdinfo]

Currently we've got PD_FLOATSIZE printing out at startup to the Pd Window for easy reference.

Once the core is fully compatible with double precision t_float, we should move the PD_FLOATSIZE to "About Pd." To do this we can easily add a method like "floatsize" to [pdinfo].