Compacttree

* Added details about the Python wrapper to CompactTree documentation

* Fixed PyPI deployment: https://pypi.org/project/CompactTree
* CompactTree's Python wrapper can now be installed with `pip install CompactTree`

* Added square-bracket operator (`tree[node]`) to extract data related to `node`
* Added `add_child` function
* Added `get_newick` function
* Removed internal use of nested iterator classes
* Removed all `auto` statements from `compact_tree.h`
* Restructured `calc_distance_matrix` return type
* Added Python wrapper
* Initial steps towards PyPI package

* Multiple updates thanks to great feedback from lczech
* Fixed Clang compilation issues
* Updated how string concatenation was being done for error messages
* Added explicit copy-assignment operators to the iterator classes
* Changed constructors to accept `const` inputs
* Added a `levelorder_iterator` class just like the existing `preorder_iterator` and `postorder_iterator` classes
* Updated cookbook and documentation to specify visit order in the various traversal iterators

* Added GitHub Action to automatically attach `compact_tree.h` to release
* Modernized documentation aesthetics
* Cleaned up repo organization
* Added cookbook
* Added function to calculate distance matrix
* Added function to bulk-replace node labels

* Added more getter / checking helper functions
* Restructured existing functions to use the new getter / checking helper functions for improved readability