Add the Jensen-Shannon Divergence

add the JSD, probably the best measure of distribution distinguishability.
rename JSD -> jensen_shannon_divergence
remove unnecessary check from JSD
break up long lines
Revamp zipped() and add atoms().
Correct error in induced_sigalg() related to zipped().
Merge pull request #26 from Autoplectic/jsd

Add the Jensen-Shannon Divergence
Merge branch 'zipped_atoms'