Added missing blank lines after sphinx directives.

Sphinx reStructured text directives require a blank line between the directive and the content (a short form is also supported where the content is on the same line):

> The directive content follows after a blank line and is indented relative to the directive start.

(from http://sphinx-doc.org/rest.html)

I'm seeing a couple of errors on one of my linux boxes when building the docs and the corresponding note boxes are not rendered. This PR adds a bunch of blank lines. It also fixes a docstring in coords.py on [lines 99-100](https://github.com/esc24/iris/blob/f1dd5a69b70cbda6e52a4997cc4417f432037994/lib/iris/coords.py#L98-100) about cell comparison which is not rendering properly at the moment.