- Add dependencies in main meson.build.
  - Add more config.h variables.
  - Create lib/meson.build and add all sources from Makefile.am
  - Add meson custom_targets for diamarshal.[ch]
  - Add dummy definition of Q_ to intl.h (turns out this was actual
    bug/oversight and not issue with meson port).
  - Add basic po/meson.build.