trivial enhancement request: Option type for apropos-variable

[Drew Adams]

'Tis not the season for enhancement requests, but this one is truly trivial.

When `apropos-do-all' is non-nil or a user uses `C-u' with
`apropos-variable' (or `apropos'), both user options and non-user variables
can be displayed in buffer *Apropos*, and they both get the same label
(button), "Variable".

Just a few lines of code would create an apropos-option button type and use
it in function `apropos-print'. This would enhance readability quite a bit,
I believe. The new label could be "Option", "User Variable", "User Option"
or whatever the right term is.