ENH: Add support for nullable integer columns to StataWriter

When attempting to export a dataframe to a Stata data file, I hit the following error due to my dataframe including variables of the Int64 dtype. 


```python
import pandas as pd

# CREATE DATAFRAME
s1 = pd.Series(2**33, dtype='Int64')
s2 = pd.Series("ABC", dtype=object)
df = pd.DataFrame({'col1': s1, 'col2': s2})

df = df.append({'col1': None, 'col2': "DEF"}, ignore_index=True)

# EXPORT TO STATA
df.to_stata('df.dta', version=117)
```
Error message: 
> NotImplementedError: Data type Int64 not supported.

My expectation is columns of dtype Int64 (i.e., a nullible INT) would end up as byte, int or float in the dta file depending on values therein.

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : 67a3d4241ab84419856b84fc3ebc9abcbe66c6b3
python           : 3.8.6.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
Version          : 10.0.14393
machine          : AMD64
processor        : Intel64 Family 6 Model 61 Stepping 2, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : en
LOCALE           : English_United States.1252

pandas           : 1.1.4
numpy            : 1.19.4
pytz             : 2020.4
dateutil         : 2.8.1
pip              : 20.2.4
setuptools       : 50.3.1.post20201107
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : 3.4.3
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.19.0
pandas_datareader: None
bs4              : 4.9.3
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.3.3
numexpr          : None
odfpy            : None
openpyxl         : 3.0.5
pandas_gbq       : None
pyarrow          : None
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.3
sqlalchemy       : 1.3.20
tables           : None
tabulate         : None
xarray           : None
xlrd             : 2.0.1
xlwt             : None
numba            : None

</details>
