pep8 and pvlib standards

[wholmgren]

There are a couple of pep8 issues. The most important ones to me are:

• no camelCase. forecast.py offenders: calcWind, addRadiation
• spaces after commas, between comparators (<), between operators (+)
• line length should be less than 80 lines.
• lowercase parameter names e.g. Half --> half, Quarter --> quarter.

Here is the link to the pvlib variable name guide:

https://github.com/pvlib/pvlib-python/wiki/Variables-and-style-rules

For consistency with the rest of pvlib, I'd like to use:

1. latitude and longitude instead of latlon
2. ghi instead of downward_shortwave_radflux
3. dni_extra instead of sp0.

[MoonRaker]

All of these issues I have addressed. Unless you see any other issues I am considering this done for now.