godoc: Provide support for simple lists.

[aghassemi]

I like to format my documentation to look like:

paragraph

-list item 1
-list item 2
-list item 3

paragraph

I can't find a way to do so, indenting the list items makes them look like code which is not correct. Putting space between list items makes each a paragraph which also is not correct.

[bradfitz]

Dup of #7873