Add comment char parameter to to_csv method
#### Code Sample
```
import pandas as pd
pd.DataFrame( ["a'", 'a"', "a,", "a#"], columns=["Column"]).to_csv("my.csv", index=False)

```
results in my.csv:
```
Column
a'
"a"""
"a,"
a#
```
(a# is not quoted)
#### Problem description

We would like to use the "#" character as comment indicator such that lines that start with the character are automatically ignored. However when fields contain the "#" character and the `pd.read_csv("my.csv", comment="#")` is used to read the CSV, then those fields are read as nan. When those fields are quoted, then they are read as literal strings (which is the behavior we want). So we want to automatically quote fields containing the comment character "#" in `to_csv`.

(the work-around we have now is set `quoting=2` (non-numeric) so by default all strings are quoted)

#### Expected Output
```
import pandas as pd
pd.DataFrame( ["a'", 'a"', "a,", "a#"], columns=["Column"]).to_csv("my.csv", index=False, commentchar="#")

```

results in my.csv:
```
Column
a'
"a"""
"a,"
"a#"
```

A more universal solution could be to allow passing a list of characters to quote for the `quoting` parameter. E.g. `df.to_csv("my.csv", quoting=['"', '#', ","]`. 

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

INSTALLED VERSIONS
------------------
commit: None
python: 3.7.3.final.0
python-bits: 64
OS: Linux
OS-release: 4.18.0-25-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.UTF-8
LOCALE: en_GB.UTF-8

pandas: 0.24.2
pytest: 4.5.0
pip: 19.1.1
setuptools: 41.0.1
Cython: 0.29.11
numpy: 1.16.4
scipy: 1.3.0
pyarrow: None
xarray: None
IPython: 7.6.0
sphinx: 2.1.1
patsy: None
dateutil: 2.8.0
pytz: 2019.1
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 3.1.0
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml.etree: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: 0.9.3
psycopg2: 2.8.3 (dt dec pq3 ext lo64)
jinja2: 2.10.1
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None
