Port to Meson

Notable differences from the autotools build:

• Dropped vapigen support (it was unused)
• Library versioning changed to use release version number rather than LT version
• --enable-valgrind is now provided by Meson’s valgrind support
• Dropped ChangeLog generation; use git log instead
• Dropped installed versioning from utilities; it reduced the usefulness of tab completion, and we can always reintroduce it if the major version number ever goes from 1 → 2
• Dropped deprecation guard support

Signed-off-by: Philip Withnall withnall@endlessm.com

Fixes: #13 (closed)