Rand uniform/normal

[zeotuan]

Close #155

• Add rand_range to Samples from ∼ U ( α , β )
• Add randn to Samples from ∼ N ( α , β )
• Rename randLaplace and randGamma to use snake case
• Add support for rand_laplace usage with mu and beta from column
• More robust implementation of rand_laplace to deal with precision error