Added support for missing value in MCMC samples.

Refactoring of the Chain type to allow for missing values (#18)

* adding union of Missing type, removed StatPlots

* work in progress

* changed in favour of #16, added unique names field

* cummean now works for missing values

* modified plotting functions to work with missing values

* added some tests for missing values, fixes for missing value

* added further tests, assertions and minor changes

* all test are now passing

v0.1.1

exported describe, fixed syntax error in mcse implementation

MCMCChain registration of version 0.1.0

Implementation of Julia types for summarizing MCMC simulations and utility functions for diagnostics and visualizations. This is the first release of MCMCChain.