Add OpenClosed01 and tweak FP doc

Author: dhardy

distributions.rs

@@ -98,6 +98,8 @@ distr_float!(distr_standard_f32, f32, Standard);
 distr_float!(distr_standard_f64, f64, Standard);
 distr_float!(distr_open01_f32, f32, Open01);
 distr_float!(distr_open01_f64, f64, Open01);
+distr_float!(distr_openclosed01_f32, f32, OpenClosed01);
+distr_float!(distr_openclosed01_f64, f64, OpenClosed01);
 
 // distributions
 distr_float!(distr_exp, f64, Exp::new(1.23 * 4.56));