tidy up code
adding new tools sub-package
adding new nanotube module for feature dev
add new helper function for chirality data
renaming module
renaming modules
updating imports from renamed modules
moving structure generating code to separate modules
removing nanotube_dev module
replace math module function with numpy wrappers
adding new code for graphene properties
adding function to compute Euler totient function
adding todo directives. update code to generate unit cell
updating algorithm for generating nanotube unit cell
fix output of variables with units
updating code
fix bugs in unit cell coordinate calculations
add new option to allow control of using units
adding new option to control use of units
allow more control over placement of vacancies in graphene