For #18, make the default ranges for float and double parameters be...

...[0, 1). Even though scaling these values to large ranges won't result
in dense choices of values, I'm not sure anyone cares. When/if they do,
we can bake it into the default floating-point generators, or expose
enough to allow custom generators with the desired properties.
Javadoc caveats for SourceOfRandomness.nextFloat/Double 2-arg.