Removed implicit lift for Directive[HNil].

In its place is the RichDirective0 type in the DirectiveSyntax
trait.
Made lift in DirectiveSyntax promotions to be Bind-friendly.

Since using Directive[HNil] instances in a Scalaz context implies
"chaining" types of use, having the prior version require and use a
Monoid seems less useful than initially thought.