.. 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.
This commit also adds the concept of "anchored" styles, which are
applied to a specific part of the line, and are tracked to always stay
applied to that specific part.
Inserting text in the middle of an anchored style extends it, and
removing the styled substring causes the style to be removed as well.
