Couple of fixes to the website docs

[kenahoo]

Hi,

There are a couple of things that need fixing on the ggplot2 website docs:

1. The docs for geom_vline() are missing the 'xintercept' aesthetic, but they mention an 'x' aesthetic, which doesn't exist. (The examples lower down on the page do talk about 'xintercept', but I missed that for a long time.)
2. There's no backlink on individual doc pages to the top-level doc page.

If there's a repo somewhere I could submit a patch, but for 1) I didn't see where the actual aesthetic list is coming from, and for 2) I wasn't sure where the code lives that's building the site.

Thanks.

[kenahoo]

I created #447 for the general solution to 1.

[hadley]

These are both fixed in the devel version with staticdocs.

[kenahoo]

Excellent, thanks.