function session(name:string):RNFetchBlobSession {
  let s = RNFetchBlobSession.getSession(name)
  if(s)
    return new RNFetchBlobSession(name)
  else {
    RNFetchBlobSession.setSession(name, [])
    return new RNFetchBlobSession(name, [])
  }
}
Get a file cache session
@param  {string} name Stream ID
@return {RNFetchBlobSession}