bumping version to v0.2.26.dev for development
updating docstrings
more docstring updates
removing empty function
porting functions from sknano.tools._chirality_funcs into sknano.nanogen._nanogen_funcs
adding new helper function to map Ch tuples to computed nanotube property
fix bug in filter_Ch which missed filtering achiral nanotube types
adding new sub-package for sturcture analysis
adding new methods for generating specific bundle geometries
docstring updates
renaming format_ext dictionary map
change import order
change docstring for tube_length to Lz
adding **kwargs to save_data methods
updating script to use nanogen structure generator classes
updating docstrings to reflect all classes are using structure_io.atoms Atom and Atoms classes
adding new Atom and Atoms classes.

Adding new StructureAtom and StructureAtoms classes for use by all
StructureGenerator clases. Replaces the chemistry sub-package
Atom and Atoms classes.
Updating code to use new Atom/Atoms classes
fixing bug in argparser argument format
bug fix