New package `outline-occur'

Hi,

`outline-occur' is a tiny package that allows users to navigate the
current buffer's outline using `occur'.  The `outline-regexp' variable
is used to find the beginning of the outline headings.  For the user's
convenience, the package also provides a configuration variable named
`outline-occur-regexp-override-alist' that allows overriding
`outline-regexp' per major mode.

When you run the `outline-occur' command, it creates an Occur buffer
with a navigable outline where you can jump between headings.

I've bound `outline-occur' to `M-s M-o' and, so far, I find it very
useful.  For instance, when working with source code, it provides a
quick overview of all functions, macros, variables and other entities
and makes it easy to jump between them.

Also, in most cases, users won't need to configure anything because many
major modes already set `outline-regexp'.

The source code repository is:

  https://github.com/jroimartin/outline-occur

If you find it useful, and given that it only depends on built-in
functionalities (Outline and Occur), would it make sense to add it to
core?  Otherwise, what about GNU ELPA?

Thanks!

        Roi