rgudhi 0.2.0

In this minor release, I:

• Added the persistence_diagram_sample class;

• Implemented the Lagragian formulation to compute the Wasserstein barycenters
  of a sample of persistence diagrams;

• Fixed CRAN warnings:

  • Incoherence of autoplot method implementation following renaming of main
    argument x into object.
  • Rectify an invalid URL pointing to the paper for BIRCH clustering.