Fix charset problems with the `R' command in eww

* net/eww.el (eww-display-html): The charset is called `utf-8',
not `utf8'.
(eww-readable): Decode the saved text correctly.
Have `R' in eww save the history

(eww-readable): Save the history before displaying so that we can
go back to the non-readable version.
Fix `eww-display-html' bug when passed an explicit DOM

(eww-display-html): Don't try to decode the text if we've been
passed in a pre-parsed DOM.
Make titles in eww prettier

(eww-tag-title): Remove newlines and extra whitespace from the
displayed title.
* net/shr.el (shr-retransform-dom): Allow several text sub-nodes.
Add missing ChangeLog entry from previous checkin