Fix apropos() output to include description

This is a trivial patch to make `apropos()` output close to what a user would expect from such a function (i.e. a list of symbol/description pairs):

>sym1 - desc1
>sym2 - desc2
>...

Since Julia documentation system is at early stages, there is no convention to write one-liner short descriptions throughout the codebase and therefore there isn't a simple way to mimic the Linux `apropos` tool behavior.

IMHO, it is better to have some description than not having at all, even if this is a provisional solution.