Add clang-format

https://github.com/kljohann/turnip.el
> This package allows to filter code through clang-format to fix its formatting. clang-format is a tool that formats C/C++/Obj-C code according to a set of style options, see Clang-Format Style Options. Note that clang-format 3.3 or newer is required.

I did not find anything similar on melpa yet and have been missing this since switching from vim. :)
byte-compiling, making the package, `package-install-from-file` and `checkdoc` produce no errors for me.