In-line heading Sass mixins

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove stray variable in mixins Sass partial

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove unnecessary html-body-spacing Sass mixin

Foundation's settings (with default `$include-html-classes: true`)
will set these sane defaults for us.

Signed-off-by: Alex Coles <alex@alexbcoles.com>