Add editorconfig, clang-format files

I've added editorconfig and .clang-format files to the repo and formatted main.c accordingly. Having a specified style at all at allows contributors to edit in their prefered style and then format their contributions to match the repo.

I chose the Google standard simply because of its compactness, but if there's a particular motivation for keeping the style used in the RR repository or any other particular style, please let me know. Personally, I find 80-wide with 2-space indents perfect for C, and the style does not waste vertical space.