scyTrack Protocol:

UDP packet to any port (default: 4711)

1-3:
	0x73 0x54 0x61; ASCII string "sTa" (scyTrack, protocol version a).

4-5:
	16-bit unsigned int: user ID on server

6-9:
	32-bit float: latitude

10-13:
	32-bit float: longitude

14-29:
	128-bit unsigned int: MD5 checksum and password hash (see below)

30-33:
	32-bit float: speed

34-35:
	16-bit unsigned int: direction

36-39:
	32-bit signed int: unix timestamp

All fields after the MD5 are optional. Speed and direction will default to
"unknown" (can be interpolated by the reading software), "timestamp" to server
time. These optional values need not be sent if you don't want to specify them,
just end your packet after byte 29, 33 or 35 if you want to. However, you cannot
leave out fields and provide others if their position is later, but you can set
them to a negative value to mean "unknown". For example, if you want to leave
out "speed", but specify "direction", set speed to a negative value.

To calculate the MD5 sum, take _all_ the fields you are about to sent, except of
course the checksum field, but including "unknown" optional fields in the right
order and append the password as not-terminated UTF8 string. Then hash it.

For example, if you're gonna send the optional "direction" (and are therefore
forced to set "speed" to a negative value and send it as well), but don't want
to send a timestamp, you would run MD5 over the following things:
  protocol identifier, uid, lat, lon, speed, direction, password