Add Clang format

[rfbird]

@dnystrom1 this is what clang format would look like

[dnystrom1]

I would like to see what clang format does to the current format before committing to it. Is there a way for me to take a clone of the current devel version and run it through clang format so I can see what it does to my manually formatted code?

[rfbird]

Yes, this branch adds the command make format which will do it if you have clang format installed. This branch also has that done, so you can see a side by side on the "file changes" page:

https://github.com/lanl/vpic/pull/92/files

There are obviously almost infinite options we can set to twiddle with things, but I am happy with how it is right now