This file was formerly named `Libraries/LibCore/puff.c` and it was not
checked by `check-style.sh` because it only checks .h and .cpp files.
Since this file was not written by us, we shouldn't check its style.
This file was also causing our Travis builds to fail.
.. and make travis run it.
I renamed check-license-headers.sh to check-style.sh and expanded it so
that it now also checks for the presence of "#pragma once" in .h files.
It also checks the presence of a (single) blank line above and below the
"#pragma once" line.
I also added "#pragma once" to all the files that need it: even the ones
we are not check.
I also added/removed blank lines in order to make the script not fail.
I also ran clang-format on the files I modified.
