<issue_start><issue_comment>Title: Add .clang-format
username_0: This is one possible way of resolving #67. This PR is pretty much just `clang-format -style=llvm -dump-config > .clang-format`.

In other words, I'm adopting the LLVM style here. If someone has strong opinions on certain options I'm happy to change them, but my thinking here was that by adopting a predefined style we can keep the bikeshedding to a minimum.

Once adopted, I can create a second PR to actually perform the reformat.
<issue_comment>username_1: Seems reasonable to me.  I agree that it's more important to have consistent formatting than it is to have a specific formatting.

It doesn't need to be done as part of this commit, but as part of the PR to perform the reformat could you also:

* Update the README with brief instructions about formatting?
* Update the CI files to flag improperly formatted code?

Thanks!