update breadcrumbs

with this update you can also use the breadcrumb layout:
    <nav class="breadcrumbs">
      <a href="#">Parent</a>
      <a href="#">Child 1</a>
      <a href="#">Child 2</a>
    </nav>

with the negligible differences of $crumb-slash being slightly smaller due to inheriting the $crumb-font-size and losing the $crumb-link-decor because it would also apply to the $crumb-slash.
Merge branch 'breadcrumb-update' of git://github.com/ascottmccauley/foundation into ascottmccauley-breadcrumb-update
updated breadcrumb defaults a bit
added reference to new markup in docs