int() policy function

Similar to string(), sometimes it is convenient to have a function which converts something from string to integer type.

Acceptance criteria:

• Policy function int() has parameter type string and return type int
• int() can be passed a real number or a string of a number with decimals
  • In both cases, the decimals will be chopped off (not rounded)
• If passed something that is not an integer or a decimal number, it should error and fail
• The new policy function should be documented in the documentation repo
• The new policy function should have an acceptance test