Fix broadcasting bug for Julia 1.0

Use broadcasted assignment syntax in Discretizers.jl

Implicit broadcasting was deprecated in 7.0.

Update for Julia 0.7 and 1.0

Make more syntax fixes for v7.0 and v1.0

Also update required versions of Julia and dependencies

Final release compatible with Julia 0.6

Don't let get_entropy return -0.0 (#18)

Also make some whitespace fixes