Support for Nested HTML Tables?
#### Problem description

Sometimes I encounter html tables that I need to parse where cells contain full-tables themselves. When using `pd.read_html` itself, this does not work quite that well. With a simple call to pd.read_html, each of these nested tables are parsed and then "inserted"/"concatenated" as rows.

```python
import pandas as pd
df_up = pd.read_html("up_pf00344.test.html", attrs = {'id': 'results'})
```

Screenshot of output as parsed:
![image](https://user-images.githubusercontent.com/2942215/66417012-f4fab680-e9b3-11e9-9630-2670d1a9a1e7.png)

#### Expected Output

I think a more natural parsing would be to parse each nested tables into their own pd.DataFrames and be inserted as objects as the value of the corresponding column.


Screenshot of table as rendered in html:
![image](https://user-images.githubusercontent.com/2942215/66417039-02b03c00-e9b4-11e9-8561-54c27f993c3e.png)

Link to file: https://gist.github.com/smsaladi/6adb30efbe70f9fed0306b226e8ad0d8


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

<details>

INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Linux
OS-release       : 3.10.0-862.14.4.el7.x86_64
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : en_US.utf8
LANG             : en_US.utf8
LOCALE           : en_US.UTF-8

pandas           : 0.25.1
numpy            : 1.17.2
pytz             : 2019.2
dateutil         : 2.8.0
pip              : 19.2.3
setuptools       : 41.2.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.4.1
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.10.1
IPython          : 7.8.0
pandas_datareader: None
bs4              : 4.8.1
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.4.1
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : 1.3.1
sqlalchemy       : None
tables           : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None

</details>
