(describe-text-sexp): Use square brackets for
button [Show] to distinguish it from the property value `show'.
(describe-property-list): Use `insert-text-button' with
`help-face' type instead of putting face in quotes, because button
is not created automatically for a list of faces.
(describe-text-properties-1): Put button-type value in quotes to
distinguish from plain text "button".
(describe-char): Display code point values in hex. Don't use
`symbol-name' for `current-input-method' because it is a string.
Use `insert-text-button' with `help-face' type instead of putting
hardcoded face in quotes, because button is not created automatically.