In a previous PR I used Buffers primarily because a user might need to write the value to another Buffer (e.g. a TCP socket). However, I found out that the ref module provides writeInt64 functions that accept strings - and strings are infinitely more usable than Buffers.
return and accept strings for int64s
I think this patch is well worth having, until we figure out a good way to parameterise return types. i.e. uint64 -> String | Number | Buffer and enum -> String | Number.