Decide on #include style

[lilleyse]

We're not totally consistent with how we include headers. What about something like this?

• Use quotation marks for header files in the same directory e.g. #include "Library.h"
• Use angle braces for everything else e.g. #include <CesiumUtility/JsonValue.h>

It would be great if clang-format could enforce this. In any case, once we agree on something it should go in the C++ Style Guide.

[kring]

Previous issue about this:
#80
Which pretty much came to the same conclusion that you wrote above. I think that's been the decision all along, we just haven't enforced it, or retroactively converted all code to that style.

In theory we don't need to put this in the Style Guide, because it's already in the C++ Core Guidelines, which are included by reference. 🤷
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#sf12-prefer-the-quoted-form-of-include-for-files-relative-to-the-including-file-and-the-angle-bracket-form-everywhere-else