started the entropy functions

I added a 'verboseTest' to the make file, this displays all logged statements during the testing period.

That allowed me to see that random bytes were being generated. I figure it has uses beyond that.

Entropy() is the first of a few entropy based functions.
The second one takes a set of [32]byte and hashes them into a single [32]byte random string that can be used to seed the random number generator.
another will take a seed and pick a random file slice for the proving storage step.

I believe all these functions belong in swarm/entropy.go