Rename distDefaultValue to sample
Finish renaming default value methods.
Begin switching default values to IO actions.
Convert more default values to IO actions.
Remove unused (and broken) sample_iid.
Add comment.
Fix structure_for_range
Switch completely to the 'strip' interpreter.
Add an evaluate_( ) operation to avoid recording dependencies.
Add a builtin to sample from an exponential.
Remove unused var.
Add builtins for random sampling from laplace and uniform distributions.
Add random actions for sampling from 3 distributions.
Make the initial conditions for uniform, exponential, and laplace random.
Put IOActions inside the Random protector.
Add gamma, beta, and normal densities.
Add definitions for sample_{beta,gamma,normal,cauchy}.
Add a sampler for beta.
Implement gamma sampler.
Implement normal sampler.