prettify the code

Currently code formatting is a mess. I already fixed some things (e.g. line endings, mix of tabs and spaces), but that's clearly not enough. I suggest to use an automatic tool for this.

clang-format looks a like a decent choice.

It's not urgent, but a must before the next fastcodeml release.

Important: All the formatting should be performed in a single commit. There should be no other change in this commit.