Initial round of probability distributions and statistical functions

doc/specs/index.md

@@ -17,6 +17,7 @@ This is and index/directory of the specifications (specs) for each new module/fe
  - [optval](./stdlib_optval.html) - Fallback value for optional arguments
  - [quadrature](./stdlib_quadrature.html) - Numerical integration
  - [stats](./stdlib_stats.html) - Descriptive Statistics
+ - [stats](./stdlib_stats_distribution.html) - Random Distributions and Statistical Functions
 
 ## Missing specs