add data files: symbols.yaml, cangjie5_express.schema.yaml, combo_pinyin.schema.yaml
support chord-typing by simulating key-ups.
squirrel.yaml: add option 'chord_duration'.
Squirrel 0.9.17 release.
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  Squirrel 0.9.17 release.
  squirrel.yaml: add option 'chord_duration'.
  support chord-typing by simulating key-ups.
  add data files: symbols.yaml, cangjie5_express.schema.yaml, combo_pinyin.schema.yaml