Add async encode/decodeString

[StrixG]

string encode/decodeString(string algorithm, string input, table options[, function callback])

Example of decoding car txd:

function decodeCallback(txdData)
  txd = engineLoadTXD(txdData)
  engineImportTXD(txd, 411)
end

local txdFile = fileOpen("car.txd")
if txdFile then
  local buffer = fileRead(txdFile, fileGetSize(txdFile))
  decodeString(buffer, "tea", {key = "TxdKey105"}, decodeCallback)
end
fileClose(txdFile)

[qaisjp]

Tested, works great. Thank you!

[Citizen01]

This PR made me remember of this issue instantly: #1152
I guess it applies on this one too ?