Add forward simulation example. Closes #71. (#86)

Author: molpopgen

Cargo.toml

@@ -21,6 +21,8 @@ bitflags = "1.2.1"
 clap = "~2.27.0"
 serde = {version = "1.0.118", features = ["derive"]}
 bincode = "1.3.1"
+rand = "0.8.3"
+rand_distr = "0.4.0"
 
 [build-dependencies]
 bindgen = "0.57.0"
@@ -36,3 +38,6 @@ name = "mutation_metadata_std"
 # Not run during tests
 [[example]]
 name = "tree_traversals"
+
+[[example]]
+name = "forward_simulation"