Improve conversion of data frames for R

[tpetricek]

The current implementation of R provider plugin does not correctly convert non-numeric data from R data frames to Deedle frames. In particular, it uses AsDataFrame from R.NET which succeeds, but converts non-numeric data to zeros.

I asked about this on R.NET forums and it should be better to do better using "factors". For more info see the R.NET discussion.

[hmansell]

I don't think factors are being converted to zeros, they are representing strings as integers (kind of like an enum). They just all happened to be the same.

In the BM dataframe conversion I think I did something to deal with factors. I can send to you if you like.