meson: add various missing options: default hinting, font dirs, config dirs
- add 'template-dir', 'baseconfig-dir', 'config-dir', and 'xml-dir' options
- add 'cache-dir' option
- add 'additional-fonts-dirs' option
- add 'default-fonts-dirs' option
- add 'default-hinting' option
Fixes #244 (closed)
All done blindly and pretty much completely untested.