Provide styling option to escape dollar signs
Jupyter Notebooks use MathJax to render text between dollar signs. Sometimes this is appropriate and sometimes it is not.

```python
import pandas as pd
df=pd.DataFrame({'A':['From $200 million to $700 million','$20+']})
df
```
<img src="https://user-images.githubusercontent.com/1804856/36501664-93cd23f6-16fc-11e8-8f74-47a47b14741d.png" width="200">

 It appears that the [official guidance](https://github.com/ipython/ipython/issues/3197/) is to use `$\$$` to render a single `$` symbol.

```python
df.A = df.A.str.replace('$', '$\$$')
df
```
<img src="https://user-images.githubusercontent.com/1804856/36502237-2c8fe2ee-16fe-11e8-8d04-54ecb2407010.png" width="200">

However, editing the data to tune the rendering is messy. I'm hoping this can be incorporated into the new [Pandas styling module](https://pandas.pydata.org/pandas-docs/stable/style.html). Perhaps something like `df.style.escape_dollar()`.

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.4.final.0
python-bits: 64
OS: Linux
OS-release: 2.6.32-696.13.2.el6.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.22.0
pytest: 3.4.0
pip: 9.0.1
setuptools: 38.4.0
Cython: None
numpy: 1.14.0
scipy: None
pyarrow: 0.8.0
xarray: None
IPython: 6.2.1
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: 0.4.0
matplotlib: 2.1.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
