Tweak CSS so really long breadcrumbs wrap nicer

Use display inline instead of floats so that manual sections with really
long titles wrap nicely instead of acting as a block.

Move the padding and font mixin onto the containing `ol` instead of the
`li`s so that the spacing underneath the breadcrumbs stays good.
Merge pull request #62 from alphagov/wrap-long-breadcrumb-titles-better

Tweak CSS so really long breadcrumbs wrap nicer