BUG: Fixed incorrect string length calculation when writing strings to 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

String types were also not being checked for excessive length, and DataFrames
with strings containing more then 244 characters were producing invalid
dta files.  Attempting to write long strings raises an error now.
TST:  windows dtype issue on testing with GH7866
Merge pull request #7862 from bashtage/stata-minimal-width-strings

BUG: Fixed incorrect string length calculation when writing strings in Stata
BUG: fixing ewma() for adjust=False and ignore_na=False
Merge pull request #7896 from seth-p/ewma_missing_weights_fix1

BUG: fixing ewma() for adjust=False and ignore_na=False
BUG: ewm*() interpretation of min_periods is off by one
BUG: do not assume 0 is in index of potential Series
TST/BUG: Rename html encoding test files.

html test_encode fails on OSX due to missing dash in ‘utf32’ encoding
string.
Merge pull request #7902 from toobaz/_get_array_list

BUG: do not assume 0 is in index of potential Series
Merge pull request #7903 from jmorris0x0/osx-html-encode-bugfix

TST/BUG: Rename html encoding test files.
Merge pull request #7898 from seth-p/ewm_min_periods_off_by_one

BUG: ewm*() interpretation of min_periods is off by one
TST: make removal tests exact for test_pytables
DOC: grammar fixes in docs
Merge pull request #7906 from mortada/grammar

DOC: grammar fixes in docs