FIX: StataReader
Fix for a bug in StataReader resulting in errors when reading Stata file with string columns

can you add a test case for this?

e.g. write a df with multi-dtypes (including object), and read back in to compare?
 Thank you for the suggestion - I was already thinking about how I can create a proper unit test, since I couldn't just use the real-world dataset where the issue happened first.

I have adapted the commit, now also containing a fix for StataWriter that was necessary to make the unit tests work.
 as an aside (and this could easily be put in 0.12)

I think it makes sense to support `index_col` in `read_stata`, and `as_index=False` in `to_stata`, though I am not sure if you can store any meta-data in the `dta` file? (e.g. to indicate this column)?
 also....I am not sure how much support stata has for dates, be sure to convert to/from `datetime64[ns]` let me know if you have any issues with this

keep in mind that `datetime64[ns]` CAN have `NaT` in there (equivalent of `nan`). You are of course free to raise if you need to if you encounter these (if stats cannot support), again I don't know the limitations
 Updated. Now also testing datetime.
 this ready to go? (the failure is unrelated to you)
 I think this is ready.
 great will merge in a bit
 thanks again!
