Add i/o options to fromBytes / toBytes

[martinheidegger]

Its nice to have with fromBytes and toBytes utils to interact with a data-stream

https://github.com/dcodeIO/long.js/blob/9448e61647f884144da26e5c13b503d586ad644b/src/long.js#L1329

However it would be useful if someone using this API wouldn't need to splice the section to be read. By adding a byteOffset it would be possible to just read a section.

bytes[byteOffset++] |
bytes[byteOffset++] << 8 |
...

Similar for toBytes

https://github.com/dcodeIO/long.js/blob/9448e61647f884144da26e5c13b503d586ad644b/src/long.js#L1277

function toBytesLE(bytes, byteOffset) {
  if (!bytes) {
    bytes = {}
  }
  if (!byteOffset) {
    byteOffset = 0
  }
  bytes[byteOffset++] = lo & 0xff
  // ...
  return bytes
}