Min/max for single integer.

[AbdulMagomedov]

It is not possible to calculate min(x) or max(x) with a single integer. It is required to wrap it in tuple:
Input: parser.parse('min(x)').evaluate({"x": 3}) or parser.parse('min(3)').evaluate({})
Result: TypeError: 'int' object is not iterable

Despite this number can be parsed:
Input: parser.parse('min(x)') or parser.parse('min(3)')
Result: <py_expression_eval.Expression object at 0x7fd984ad8f10>