Log Message:
Update to 16.2

Chagneglog:
* Remove GNU Emacs 22 support
16.1 supports GNU Emacs 22.

* Add GNU Emacs 26 support
Use encode-coding-string() instead of obsolete string-make-unibyte().

* Support Ruby 2.4
Support bayesian/bskk with Ruby 2.4.

* Select window management
skk-candidate-buffer-delete-other-windows as nil disables
windows management.

* Candidates display with SPC key
skk-show-candidates-nth-henkan-char should be 2 or greater.

* A number of Candidates
Specify a number as skk-henkan-number-to-display-candidates.
Do not use skk-henkan-show-candidates-rows, it is obsolete.