Simple integer calculator.

This program is a simple calculator which has a stack of integer values. It defines commands to:

• Push integer values on the stack. These values are either in decimal or hexadecimal (0x prefix)
• Do simple operations on top most values on the stack. Operands are popped from the stack and the result is pushed back.
• Select the format of the output result and list the content of the stack.

Source file: calc.c