I like to have a mode where CONTAINS_NOTDEF and CONTAINS_DOTTEDCIRCLE are not
returned. Abused a value of -1 for that. hb-shape now uses it. Fixes two
of the six tests failing with --verify in test/shaping/run-tests.sh.
The new test suite runs tests included under
hb/test/shaping/tests/*.tests, which themselves reference
font files stored by sha1sum under hb/test/shaping/fonts/sha1sum.
The fonts are produced using a subsetter to only include glyphs
needed to run the test.
Four initial tests are added for (Chain)Context matching,
of which three currently fail.