Remove duplicate FSharp.Formatting package
Change csv row representation and improve error handling

* The representation was previously just a string[] and on each cell access the conversion was being made (possibly repeatedly)
* Now it's a tuple, and each row is converted as a block (but still each row on deman)
* This improves the display on F# interactive and the debugger, and allows the csv rows to better display on tools that use reflection and support tuples, like generic data grids hooked into fsi
* It also allows the IgnoreErrors flag to ignore rows with different data types on the columns, and not just different numbers of columns
* With this change we achieve feature parity with the csv provider of TryFShrap.org
Dynamic lookup for CSV (fixes #64)
Simplify CSV dynamic API
Support customization of missing values (fixes #55)

In addition to the already supported "#N/A", add "NA" and ":"  to the defaults.
"NA" is the default in R datasets, ":" is the default in EU and UK government datasets
Missing updates to the unit tests
Improve display of rows in fsi

It turns out using ToString works exactly the same when displaying a single value, but not when displaying a seq or array of them
Improve docs
Merge pull request #122 from ovatsus/CsvImprovements

Change CSV row representation, improve error handling & support for dynamic lookup