Merge pull request #50 from drincruz/release/0.3.0

syncing down release/0.3.0 changes
added tree_height()

this closes #51
Merge pull request #53 from drincruz/feature/utils/tree_height

added tree_height()
added unit tests for tree_height()

This closes #54.
Merge pull request #56 from drincruz/feature/unit_tests/tree_height

added unit tests for tree_height()
added tests for insert_node()

This closes #57.
Merge pull request #58 from drincruz/feature/unit_tests/insert_node

added tests for insert_node()
added small example for tree_height()

this closes #55.
Merge pull request #59 from drincruz/feature/docs/tree_height_examples

added small example for tree_height()
v0.4.0 version bumps and release notes
Merge pull request #60 from drincruz/release/0.4.0

Release/0.4.0