run source through clang-format

[mbunkus]

Due to all the changes the sources become rather chaotic wrt. style. I think we should come up with a canonical set of settings for clang-format & format both libEBML & libMatroska with them for release v2.0.

It's possible that this won't work well due to the use of macros, though. Nevertheless, I think we should explore its use.

[robUx4]

I agree, especially if it's something we can run (and thus ensure later in the CI). The current styling is definitely all over the place.