Simple spreadsheet processor

• If cell starts with "!" it will be calculated as RPN expression (supported operators + - * /)
• In expression, cells can be referenced as $<num>
• Dependent cells are tracked for "computed" cells, so if some cell value has been changed or recomputed, only dependent cells will be recomputed
• Complex circular references aren't handled, so they will hang your browser

Example of computable expression: !$4 3600 / $5 *