Distribution should not include generated config.xsl

[martindholmes]

At the moment, any config.xsl generated by e.g. processing the documentation is included in the distribution; obviously this is wrong.

[martindholmes]

There are many more things we can exclude from the dist, so I'm going to add to the PR.

[martindholmes]

Initial work merged for a release, then I'll take another look to see what else might be excluded.