[io] csv parser cannot parse arraymancer csv files
Related to #162 but deserves to be its own issue.

Given the existence of `readCsv` and `toCsv` it's not unexpected to think that arraymancer could parse its own csv files. Unfortunately, this is not possible as the csv files generated by arraymancer contain the dimension information for each index as two columns. Thus, parsing an arraymancer csv file leads to a `(N+1)xM` tensor, where `N` is the number of dimensions of the original tensor and M the size of the tensor. 

We should have an option in `readCsv` `isTensor` or something like this that knows about the arraymancer layout and parses it back to the original layout.