Add optional second base argument to int DSL function

[johnkerl]

For issue #1241

int  (class=conversion #args=1,2) Convert int/float/bool/string to int. If the second argument is
omitted and the first argument is a string, base is inferred from the first argument's prefix. If
the second argument is provided and the first argument is a string, the second argument is used as
the base. If the second argument is provided and the first argument is not a string, the second
argument is ignored.

Examples:
int("345") gives decimal 345 (base-10/decimal input is inferred)
int("0xff") gives decimal 255 (base-16/hexadecimal input is inferred)
int("0377") gives decimal 255 (base-8/octal input is inferred)
int("0b11010011") gives decimal 211 which is hexadecimal 0xd3 (base-2/binary input is inferred)
int("0377", 10) gives decimal 377
int(345, 16) gives decimal 345
int(string(345), 16) gives decimal 837