Update to 2.6.7
    
    - If the first candidate is exactly the same as the typed string
      prefer longer candidates (Extends inline completions automatically)
    - Move README to README.md and use some markdown to make it look better on github
    - When showing similar emoji in the lookup table, show the list of keywords
      which matched only when debugging is on
    - Update emoji annotations from CLDR
    - More unittests, restructure test files, move some doctests to unittests
    - Add a utility class KeyvalsToKeycodes to find ibus key codes
      instead of hardcoding them
    - Add ceb to CLDR_ANNOTATION_FILES