test => factorial
test => factorial division
test => division with large numbers
Merge branch 'factorial_division'
add test into all-tests.html
test => plus
test => operand arguments
test => minus
refactoring => change operator return function instead of value
test => digits
test => times
test => division
fix bug => return zero after expression eval
refactoring => dynamic method definintion
Merge branch 'calculating_with_functions'
add test into all-tests.html