adding some docstrings
adding new linear algebra transformation functions for rotating points about arbitrary axes
updating call to rotation_matrix
updating docstrings and import order
adding __repr__ method to Nanotube class
Making DefectGenerator the parent class of VacancyGenerator
Adding/removing classes for future dev
adding new module for polyhedra containers
adding vac_bounds dict to set bounds on vacancy locations
adding unicode to all instance checks for str type