Run list: "foo" now expands to "foo::default"

This is a breaking change. Before, foo was expanded to <cookbook>::foo.
Now you need to specify ::foo to get the same result.

This change brings chef-runner's behavior in line with Chef's run list
format, where foo is also expanded to foo::default.
Better naming
Update changelog
Merge branch 'runlist-standard'

* runlist-standard:
  Update changelog
  Better naming
  Run list: "foo" now expands to "foo::default"