Remove a done item from the TODO

I've added the note for libcangjie and pycangjie, it's unnecessary for
ibus-cangjie.
Remove an item from the TODO

I moved it to a bug report:
    https://github.com/bochecha/ibus-cangjie/issues/1
Remove future stuff from the TODO

I moved them to bug reports, in their own special milestone:
    https://github.com/bochecha/ibus-cangjie/issues?milestone=2
Remove the TODO file

Everything which remained has now been moved to bug reports, in the 1.0
milestone:
    https://github.com/bochecha/ibus-cangjie/issues?milestone=1
cangjie: Pressing space twice on multiple candidates

When pressing space, the user sometimes gets multiple candidates.

When that happens, if the user presses space again, we should commit the
first candidate.

fixes #7