Fix cache using incomplete key

This manifested when you had a template.cshtml and a ja\template.cshtml. If I run english docs then japanese docs on F# Data on the same process, the japanese docs would get the english template
Improve debug info
Make FsiEvaluator thread safe so we can use Array.Parallel on Literate.ProcessDirectory
Merge pull request #216 from ovatsus/master

Fix cache using incomplete key