(TK-83) Add :enable-trailing-slash-redirect option

Add new :enable-trailing-slash-redirect option to the options map
for all service functions that add handlers. When true, all
requests made to the handler without a trailing slash will be
redirected to have a trailing slash. Defaults to false.
@KevinCorcoran I think that's a little misleading. It makes it sound like it will do a redirect when a trailing slash is present, when in fact the redirect occurs when no trailing slash is present.

Maybe `redirect-to-trailing-slash`?