Support broadcasting Holfuy API data

[bzed]

Only tested with the test API credentials from holfuy as I don't have a real key/password yet, but works well so far.

I think the holfuy and WU code should be generalized a bit more, I've started to put the http request code into a function so it can be shared at some point, but I did not have the time for a longer rewrite.

Also the api description about the rain values was not clear about the timeframe, so I skipped rain values for now.

[rvt]

Just a challange question: holfuy is little coverage from what I see, is it worth to add and what is the quality of their data?

[bzed]

Just a challange question: holfuy is little coverage from what I see, is it worth to add and what is the quality of their data?

No idea what you are looking at, buy holfuy is (was!?) the de-facto standard weather station on paragliding sites in the alps. The data quality depends on the exact location of the sensor as usual. And yes, its worth adding.