Add Sass/LESS mappings for Weather Underground API

[chriseverson]

This commit adds Sass and LESS mappings for the Weather Underground API.

Neither has been compiled down to CSS in this commit as I wasn't sure on the exact preferred compile settings for this project.

[erikflowers]

This looks good, I will take it over and recompile and upload.

I use Codekit to compile and work on the project: https://incident57.com/codekit/, which is simple for the weather API mappings, but it gets a lot more complicated with the main files that run through the ./wbuilder app in the _builder folder that exports the css, jade, and index files as well.

So you did the right thing.

[erikflowers]

There were some issues with the Less file, the syntax wasn't right, it was sort of a mix of Less and Sass. So I fixed it and compiled, so you'll want to replace your files with the new ones. I also added a -wu prefix since some of the classes would overwrite the Weather Icons classes

https://github.com/erikflowers/weather-icons/blob/master/less/mappings/wi-wunderground.less
https://github.com/erikflowers/weather-icons/blob/master/sass/mappings/wi-wunderground.scss

But thanks for doing this, was easy to fix and add.