Updated gitignore rules

Made sure no X509 certificates are committed accidentally.
Corrected Hello handling in both client and server

client.go:
  Ensured that a Hello is sent upon connection, in order to
  test connection and send SCAMP version number and
  user agent.

request.go:
  Enabled communication of packet type within the library
  so that the server can identify Hello packets.

server.go:
  Ensured a Hello packet has been received, and its scamp
  version validated, before any requests are served.

  Furthermore, the client's user agent is now stored in the
  connection state, so it can be presented to the server
  with all requests.

  Also removed unnecessary use of scamp.Error.SetFlags
  for fatal errors, where the flag had already been set by
  scamp.NewError(false, ...).
Added user agent passing.

The user agent stored from the latest Hello is now added to the
server-visible request, as originally intended.