Add clang-format file

Also run it across the whole tree to get everything using the One True Style.
We don't yet run this in an automated fashion as it's a little slow, but
there is a snippet to do so in makeall.sh.

LibCore/CFile.cpp

@@ -1,7 +1,7 @@
 #include <LibCore/CFile.h>
-#include <unistd.h>
 #include <fcntl.h>
 #include <stdio.h>
+#include <unistd.h>
 
 CFile::CFile(const String& filename)
     : m_filename(filename)