added check_coordinates and get_transform to util.py
added Resource class
implement __getitem__ in the Resource class
refactoring: added returnboard package; WIP: use Resource instances for all objects;
document util.parse_color method
fix color parameter handling
WIP: refactoring modules: fix imports in test cases
fix: super __init__ call needs self parameter
make printing resources prettier
WIP: use resources for components; improve parameter names;
color should be tuple
resources should only be reserved when writing geometry
added include_empty parameter to Resource.print_resources
resources can and should be reserved in the init phase
WIP: use resources for all components: refactor the frame
board: allow providing orientation using names (w_dir, l_dir, t_dir)
Board: fix checking of (w_dir, l_dir, t_dir) parameters
Board: fix checking of (w_dir, l_dir, t_dir) parameters
fix doc typo
added Material class; use it instead of color parameters;