CSV export extension

[pierstitus]

Add a CSV export extension in the examples/extensions dir. Closes #76

One CSV file per day is saved.

extvar configuration:
"outpath": path where to save CSV files, default: "/home/pi/grottlog"
"csvheader": comma separated string with fields to store, defaults to all available fields

To be able to convert the data to standard units the detected data layout is added to the conf variable as conf.layout.

[johanmeijer]

Nice! I am going to test it!. This is why I created the extension feature. I am glad somebody is doing something useful with it ;)

Also nice that you make changes to the original grott coding to improve the use of extensions.

[johanmeijer]

I will commit this to the master and also applies it to the 2.7 (2.7.1) branches. I will update the wiki (add it on the extension page or create separate page for it) and describe it in the readme.

Thanks!!

[pierstitus]

Nice, thanks!
On the wiki there's a small typo, a double quote before outpath on the line:

extvar = {""outpath": "<path to your CSV files>", "csvheader": "<your csv header>"}

I'm using the following as a quite complete log without too much zeros or double data. But with different inverters that will differ too.

"csvheader":"time,pvpowerin,pv1voltage,pv1current,pv1watt,pv2voltage,pv2current,pv2watt,pvpowerout,pvgridvoltage,pvenergytoday,pvenergytotal,totworktime,pvtemperature,pvipmtemperature,epv1today,epv1total,epv2today,epv2total"