Remove yon-actions module.

* yon-actions.el: Delete it.

* yon-chan.el: Remove yon-actions include.

* yon-formatting (yon-format-post-image): Use renamed function.

* yon-navigation (yon-display-image-other-window): Move and rename function.
Improve docstrings for yon-navigation.

* yon-navigation.el: Rewrite docstrings.
Add docstrings for yon-communication.

* yon-communication.el: Add docstrings.
Improve docstrings for yon-structures.

* yon-structures.el: Add/rewrite docstrings.
Improve docstrings and refactor yon-utils.

* yon-utils.el: Add/rewrite docstrings.
(yon-get-closing-point, yon-replace-string-section: Refactor.
Add yon-current-buffer-posts function.

* yon-navigation.el (yon-current-buffer-posts): New function.
(yon-jump-posts, yon-jump-to-local-post): Use new function.
Merge remote-tracking branch 'refs/remotes/upstream/master'