gracefully shut down other processes
makes program work without file argument, opening an empty file
adds range support using [A1()+A5()] syntax
moves README to README.md for better visualization in supporting tools
add empty values for dependencies
do some rudimentary cyclic dependency check
adds error output, better dirty tracking, allow to save files without preamble
track dirty state, display file and dirty state
adds click to edit (RMB), don't save empty cells