Add support for fsi evaluation in literate scripts

This should make a good start on https://github.com/tpetricek/FSharp.Formatting/issues/19.

I have not included any documentation or demo, but the test showcases and checks all the features - they are pretty much as we discussed in the issue above. Also, to get you interested, here is a gist with the original literate script, the html output, and how to generate the latter from the former: https://gist.github.com/kurtschelfthout/9021581

Issues:
- no LaTeX support, but should be trivial to add in Transformations...just need to take OutputKind into account and choose an appropriate formatting. It's been ages since I've used LaTeX so I couldn't be bothered to install & test it.
- not tested with Markdown scripts. Would expect few, if any, problems.
- no documentation.

Hope you can accept this despite those shortcomings - even with these they are enough to scratch my itch (and so hopefully other's as well) and it's unlikely I'll have a decent amount of time to look at this further in the following weeks.