Finished C# documentation for data frame

 * I finally finished the C# documentation for the `Frame<R, C>` type, so that's the main thing in this pull request. 
 * I also updated F# Formatting to a more recent version (there was a slight change in the package, so it's best to do this while I still remember what to change :-)).
 
I already published the new documentation and it is available here: http://bluemountaincapital.github.io/Deedle/csharpframe.html