* put parsePacketData in deserializer and createPacketBuffer in serializer
* remove packets from the index and expose readPacket instead
* load packets when needed in various files
* make tests test every supported version
static cross version of #234, fix#65, fix#240
also create a few other files containing common information and functions :
* mcHexDigest.js which contain the function of the same name used in both createClient.js and createServer.js
* ursa.js which handle the abstraction on top of ursa and ursa-purejs : used in both createClient.js and createServer.js
* version.js used in index.js, createClient.js and createServer.js
