Update __init__.py

Proposal to update add_bone and get_vertex_weights functions

Added lines to add_bone function that set the new bone as a child to the skeleton root

The get_vertex_weights function appears to be set to initialize an empty list of lists, and then return it.

Modified get_vertex_weights function to return a list of dictionaries in the format {[v_idx: {b_idx: weight}]} where v_idx is the vertex index and b_idx is the bone index.