Check overflow in integer literals

Make this:
>> 9'999'999'999'999'999'999
== 9223372036854775807

become:
>> 9'999'999'999'999'999'999
** Syntax error: invalid "integer" -- "9'999'999'999'999'999'999"
** Near: (line 1) 9'999'999'999'999'999'999

https://github.com/zsx/r3/issues/8