R6causal 0.7.0

• Added R6 class ParallelWorld to enable more general counterfactual simulations.
• Improved output control for simulations.

R6causal 0.6.1

• A minor change due to change in the igraph package.

R6causal 0.6.0

• The first version submitted to CRAN.
• Added a NEWS.md file to track changes to the package.