add already merged contributions to next whatsnew

[wholmgren]

A few users have made contributions that didn't get logged in a what's new document. Making an issue here so that we don't forget this. Probably easiest if I add the notes once #93 is merged. I believe that the following PRs need to mentioned:

• Update pvsystem.py #112
• Appveyor #111
• avoid the conda/travis/pip/scipy mess with a simple skip #109
• Use conda on readthedocs #108
• fix for https://github.com/pvlib/pvlib-python/issues/102 #103
• Using cec-modules with sapm #122