For clojure.kak and haskell.kak, set extra_word_chars on the buffer
and not the window, so that the buffer's word db is updated correctly
for word completion.
Document this.
Also, minor refactor of clojure.kak.
Closes#3108
Indentation can be different depending on the first word of list forms. The
indent hook uses `e` from inside the parent to select the first word for
testing whether it is a special word; however, in the case of a one-character
symbol, this selects to the end of the *next* word.
This rejects such selections.
