Meson build support

This merge request adds Meson build support to libdvdnav. I've left the soname version as it is for now, but I change it if necessary.

In order to get CI working, I've added a libdvdread.wrap file. This uses Meson's built-in subproject support to download and build libdvdread if it isn't found via pkg-config, similar to the way libbluray includes libudfread as a git submodule. Currently the wrap file points to the master branch of libdvdread, but I would suggest updating it to keep track of the latest stable version once it's released.

I've also got a branch which adds fixes for building with MSVC, but I think it needs further review so I'll make it a separate MR.