pd.read_csv does not allow passing valid delimiters when using sep=None
#### Code Sample, a copy-pastable example if possible

Using a sample file of:
```
email
test@gmail.com
test2@yahoo.com
test3@microsoft.com
```

```python
import pandas as pd

pd.read_csv('email.txt', sep=None)

Out[24]: 
                          e  ail
test@g               ail.co  NaN
test2@yahoo.co          NaN  NaN
test3@          icrosoft.co  NaN

```
#### Problem description

There is no way to pass the 'delimiters' argument to csv.Sniffer.sniff when using pd.read_csv(sep=None) causing an invalid detection of the delimiter in files with only a single column.

#### Expected Output
```python
                 email
0       test@gmail.com
1      test2@yahoo.com
2  test3@microsoft.com
```

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

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.6.8.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
machine          : AMD64
processor        : Intel64 Family 6 Model 58 Stepping 9, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.None

pandas           : 0.25.1
numpy            : 1.16.1
pytz             : 2017.3
dateutil         : 2.6.1
pip              : 19.0.1
setuptools       : 40.6.2
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : 1.7.6
blosc            : None
feather          : None
xlsxwriter       : 1.0.4
lxml.etree       : 4.1.1
html5lib         : 1.0b10
pymysql          : None
psycopg2         : None
jinja2           : 2.10
IPython          : 7.2.0
pandas_datareader: None
bs4              : 4.6.0
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : 4.1.1
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : 2.5.14
pandas_gbq       : None
pyarrow          : None
pytables         : None
s3fs             : None
scipy            : None
sqlalchemy       : 1.3.8
tables           : None
xarray           : None
xlrd             : 1.2.0
xlwt             : None
xlsxwriter       : 1.0.4
</details>
