Improve multi-language support (take 2)

[jaxter184]

Sorry to clutter the pull requests; seems like I accidentally pushed the wrong commit to my fork, and I'm not sure how to reopen the old PR.

I squashed the config.languages | length change into the first commit, and added a second (tentative) commit changing the default example to show the multi-language capabilities. I'm a little uncertain whether the extra config options are the best move though. I feel like multi-language support is a bit of a rare case, and 99% of people will just want a one language thing. It adds a lot of extra information, so maybe it would be better to put this information in the README? or in a second file as a separate guide?

[jaxter184]

Is there anything else I need to do to get this merged?

[jaxter184]

Failed during stage 'building site': Deploy directory 'public' does not exist I'm not sure what this means

[Keats]

Don't worry about that