Stick breaking

[cscherrer]

• Add experimental module with stick_breaking_process submodule containing:
  • StickBreaking struct representing a stick-breaking process
  • StickBreakingDiscrete struct representing a discrete distribution based on a stick-breaking process
  • StickSequence struct representing a sequence of stick breaks
  • BreakSequence struct representing a sequence of break points
  • posterior method on StickBreaking to compute the posterior distribution given data
  • Various helper methods and trait implementations
• Update ConjugatePrior
  • Change LnMCache to MCache
  • Change LnPpCache to PpCache
• Split Rv into Sampleable and HasDensity
• Add Process generalizing Rv
• Add Parameterized trait
• Add impl<X: Booleable> ConjugatePrior<X, Bernoulli> for UnitPowerLaw
• Add ConvergentSequence implementing Aitken's delta-squared method
• Add sorted_uniforms helper function
• Minor stylistic changes suggested by Clippy

[BaxterEaves]

Looks great -- thanks! Couple of minor comments!

[BaxterEaves]

LGTM!