support generic GPS tackers

Many GPS loggers/trackers allow to publish points by performing a GET request to arbitrary HTTP server.

This "tracker" allow to store it in a plain text and retrive.

The only point is to add &u=USER argument, where USER is an arbitrary string to put apart possibly multiple users of the service.

Any arguments without value (&arg&), with empty value (&arg=&), or with values of 0 and 0.0 are ignored and not saved into the log.

When invoked with only &u=USER argument, it will display the last point reported.

The current implementation supposes the use of GPS Logger.

Graphics and geocoding by Yandex and Sputnik free API.

# 2018-03-15 09:35:34 +0300 user1
/ REMOTE_ADDR=1.173.86.123
lat=5.75641094
lon=7.56704068
time=2018-03-15T06:35:34.000Z
s=3.18
sat=12
alt=139.0
acc=10.618999481201172
prov=gps
# 2018-03-15 09:36:45 +0300 user1
/ REMOTE_ADDR=1.173.86.123
lat=5.756657
lon=7.5658873
time=2018-03-15T06:36:25.226Z
acc=24.836999893188477
prov=network

This picture was grabbed from GPS Logger site: