Improve docs, merge pull requests & fix some bugs

This finishes most of the work items that I was hoping to finish before having a new major release. 

 * Merge pull request adding an F# implementation of `Deque` from @forki. It looked like the new deque was a bit slower, but I think that might just be because I tested it with Debug build. Anyway, I made some optimizations in other parts of the code (https://github.com/tpetricek/Deedle/commit/87547756a4477dd7a3df28930fd703d6a23d6006). I also added some FsCheck tests and found - I think - a bug with handling of missing values (see the test and fix here: https://github.com/tpetricek/Deedle/commit/e2f5a26d7bab85335c4a6a099554f71dc9a5a425)

 * I did some bug fixes in the `Series.shift` and `Series.diff` function - @adamklein discovered them and fixed some in a recent checkin, but they were actually a bit deeper (see https://github.com/tpetricek/Deedle/commit/9443c3994336fb87e9d8ae7969e8594639060423). There was also a bug with `indexWith` (fixed here: https://github.com/tpetricek/Deedle/commit/176f7cd9489f118902e02098a147722497a21d61) and saving of CSV using non-standard cultures (https://github.com/tpetricek/Deedle/commit/a75c01c2ed79bd16ed7870fa59b24bfe659832b2).

 * The rest of the work is improving documentation - I want to have nice generated docs for `Stats`, `Frame` and `Series` module (generated from the inline code comments), so I did a lot of reorganization and adding comments there (https://github.com/tpetricek/Deedle/commit/176f7cd9489f118902e02098a147722497a21d61).

  Another new thing in the documentation is that F# Formatting can now automatically run the scripts and embed results (frames and series as HTML tables, charts as images). This is done in https://github.com/tpetricek/Deedle/commit/b8aa163cda5b261a780c636d4cca3d7566ee7aa8. Search for `(*** include-value: ... ***)` and `(*** include-it: ... ***)` to see this :-)

There are two more things that I'd like to finish in the documentation (comments for `Frame` module and tutorial showing the `Stats` module), but I think that's it for the next release. The other work items I have are mainly additive or internals-related, so I think we can do them later (and also switch to faster release cycle for NuGet)

I also pushed an "alpha" release to NuGet so that others using Deedle can have a look and report any issues: http://www.nuget.org/packages/Deedle/1.0.0-alpha. I would wait a week or so and then release a final version. When it happens, should we officially mark this as the "1.0" release?