Explain in release notes that vertices must be labelled if you want to sample from them.
### Version 0.0.19 ###
* Added `get_vertex_by_label` to `BayesNet`
-* Added optional param `label` for all vertices in Python (e.g. `Gaussian(0., 1., label="gaussian")`)
+* Added optional param `label` for all vertices in Python (e.g. `Gaussian(0., 1., label="gaussian")`). Now you must label vertices you are sampling from, otherwise Keanu will throw an exception.
* Reorganised the factory methods for building `PosteriorSamplingAlgorithm` objects. The following are available and give you access to either a default implementation or, when you need more control over the configuration, a Builder object:
* `Keanu.Sampling.MetropolisHastings`
* `Keanu.Sampling.NUTS`
