Ufo2ft

- [featureWriters] Support insert marker in the middle of a feature block (873)
- [cursFeatureWriter] Respect direction suffix when setting lookupflag (876)

- Rewrite old kern writer to pull in some changes made in the newer one (870)
- markFeatureWriter: Support contextual anchors (869)
- markFeatureWriter: Support contextual ligature anchors (871)

- [featureWriters] Ensure CursFeatureWriter comes first, before kerning mark feature writers; in some non-HarfBuzz implementations the GPOS lookup order matters (864).
- [kernFeatureWriter] Ignore zero-valued class-class kerning pairs when generating variable kern feature as they are no-op (866).
- Take discrete axes into account when checking for feature compatibility across masters (867).

- cursFeatureWriter: Remove stray print()

- kernFeatureWriter: Support sparse masters (859)
- cursFeatureWriter: Support multiple entry/exit anchor pairs (863)