Int128.toString

void toString(Writer, FormatSpec)(scope ref Writer sink, scope const ref FormatSpec fmt) const

Formats Int128 with either %d, %x, %X, or %s (same as %d).

`sink`	Output range to write to.
`fmt`	A `FormatSpec` which controls how the number is displayed.

FormatException if the format specifier is

not one of 'd', 'x', 'X', 's'.