Issue#144-fixed the azimuth calculation of rotated PV panel

[mayudong]

The results are consistent with PVsyst.

Also the tests are updated to cover this issue

[wholmgren]

Thanks. I'll make a few line comments.

Do you want to rerun the tracking tutorial and commit the results? I can also do this after the merge.

[wholmgren]

It will be more clear what's actually being tested if you make these assignments when the object is created.

[wholmgren]

Please also rebase your changes on the new master, add a note to the bug fix section of the 0.3.1 whatsnew file, and add your name or username to the contributors section of the whatsnew file.

[mayudong]

I have followed most of your comments. However, I would love more clarifications on "Please also rebase your changes on the new master"
Best

[wholmgren]

I merged #141 after you forked pvlib. The git rebase command will reapply your new commits on top of the latest version of pvlib. You will need to run something along the lines of

git remote add upstream https://github.com/mayudong/pvlib-python.git
git fetch upstream
git rebase upstream/master

Then resolve the conflict in whatsnew and commit the results. You'll need to add the -f flag to git push to force push the changes to your github branch. Give this a try but if it's too much hassle then I can manually resolve the conflict.

[mayudong]

I have addressed all your comments. Please double check and merge back at your convenience.
Best
Yudong

[wholmgren]

I checked out @mayudong's branch and reran the tracking tutorial. Here's the new figure that shows the tracking parameters for different surface tilts

And here's the same figure from the v0.3.0 version

I should have realized that this behavior wasn't right when I first wrote the code. Thanks for catching it. I'll push the new tutorial next.

Closes #144