Allow full range for nextInt and nextLong.
Add an immutable random Generator and Uniform.
Add Gaussian implicit distribution.

This also includes instances for Float, Double and BigDecimal.
Add tests for gaussian distributions.
Merge remote-tracking branch 'upstream/master' into topic/immutable-generators
Fix bug in Quaternion ScalaCheck test.
Fix bug with Generator#copy and gaussian state.

Previously, copied generators would have a 50% chance of returning
different values for nextGaussian. This commit fixes that.