v3.0.13

Support vcpkg build system (#717)

First step towards transitioning away from cxx-common's `pkgman.py` dependency management system towards compatibility with and use of vcpkg (https://github.com/microsoft/vcpkg) to manage dependencies.

This commit attempts to support both the new and old build systems until we can phase out the old completely.

Please see the updated remill, anvill, and trailofbits/cxx-common repositories to learn how to fetch the required dependencies.