format **/*.c with clang-format-3.5

format **/*.c with clang-format-3.5

This has multiple effects:

1) The i3 codebase is now consistently formatted. clang-format uncovered
   plenty of places where inconsistent code made it into our code base.

2) When writing code, you don’t need to think or worry about our coding
   style. Write it in yours, then run clang-format-3.5

3) When submitting patches, we don’t need to argue about coding style.

The basic idea is that we don’t want to care about _how_ we write the
code, but _what_ it does :). The coding style that we use is defined in
the .clang-format config file and is based on the google style, but
adapted in such a way that the number of modifications to the i3 code
base is minimal.