Lexer doesn't recognize Int64 minimal value

[fatmage]

Writing Int64 minimal value -9223372036854775808L gets you an out of bounds error as the absolute value exceeds the max value of Int64.

> let a = -9223372036854775808L ;;
fatal error: Integer literal 9223372036854775808 exceeds the representable range
   | let a = -9223372036854775808L ;;
   |          ^^^^^^^^^^^^^^^^^^^
   | 
> let a = -9223372036854775807L - 1L ;;
> a ;;
: Int64
= -9223372036854775808L
> 

[ppolesiuk]

I'm not sure if it is a bug or a feature. For simplicity, Fram doesn't have negative literals: positive literals with unary operators are enough in almost all cases. Almost... except minimal integer values. However, these can be defined in the standard library.