Update to published API and some fixes

[tobi]

Windguru published some API docs and I went ahead and switched to those.

There were actually some bugs that were fixed along the way. The main change is that we now use their salt+station+pass MD5 hash as auth.

Some bug fixes:

• interval was set to 1 second, but was actually supposed to be the post_interval period which is 5minutes by default.
• percip_interval was also set to 1, switched the percip parameter to hourRain and pass the interval as 1h

One observation: windguru seems a lot happier with more frequent updates, so I added the config parameter for 60s updates to the readme by default.
Also went ahead and mentioned the UID/Station ID thing that was suggested in #2, so this Closes #2 if merged.

[claudobahn]

Thanks for doing this, I'll try to take a look soon.

I haven't looked, yet, but I suspect this will require station owners who are up and running with the current plugin to change their station type on the Windguru side? If so, this probably warrants a clear "breaking change" notice in the README.

[tobi]

No need to change the station type, it's been working nicely with 60s interval updates here: https://www.windguru.cz/station/3609 - the station is setup as normal weewx type

[tobi]

you should merge it!