BUG: Fixed incorrect string length calculation when writing strings in Stata
Strings were incorrectly written using 244 character irrespective of the actual
length of the underlying due to changes in pandas where the underlying NumPy
datatype of strings is always np.object_, and never np.string_. Closes #7858

@bashtage I would generate some files in stata in both formats and add to the repo as well. Is this a bug fix or an API change?
 @jreback I'm not sure a Stata-generated file would add much - the bug is in `StataWriter` which no longer correctly identifies string sizes, and so defaults to the maximum size 244 for all strings. 

I think I've decided this is a bug since the code does not appear to do what is intended (even though it is functional).
 ok, that's fine then
 Hold off a while on the merge - I need to check what happens for longer strings (> 244, which are a problem)
 I c, it was being actually set before. never saw that.
 @bashtage np. lmk

you truncate / warn / raise for too long strings
 Just want to make sure it is still working correctly, and be certain there is a test for that case.
 Definitely not working for longer strings, so more work needed.  The files generated actually crash Stata 12...
 looks like you were truncating before (which is fine I think) (maybe with a warning thougH)
 I have raised it as an error in the PR.  Not completely sure that it the correct behavior though.
 stata has  max of 244, right? so then that is ok
 I just checked 0.14.1 - attempting to write a 500 character string produced no warning or error, and outputs a corrupt stata file (that segfaults Stata)
 ok gr8! so raising is good (put this fix in API changes, even though its really a bug -fix). in theory its more visible there.
 @jreback I think this is ready, subject to doc/other checks
 @jreback Hopefully ready now
 gr8 ping when green
 @bashtage awesome as usual!
