pct_change() scale is actually 0-1, i.e. fractional_change()
#### Code Sample, a copy-pastable example if possible

```python
# Your code here
>>>import pandas as pd
>>>a=pd.Series([0,1,2,3,4])
>>> a.pct_change()
0         NaN
1         inf
2    1.000000
3    0.500000
4    0.333333
dtype: float64

```
#### Problem description
This is fraction change and not percent change.  

Dictionary definition of percent is 
"One part in every hundred."


Either change the documentation  to state that it is fractional change and not percent change with the formula (for backward compatibility) or rename it (to get rid of the obvious error).

#### Expected Output
>>> a.pct_change()*100
                   Val
2017-12-31         NaN
2018-12-31  100.000000 %
2019-12-31   50.000000 %
2020-12-31   33.333333 %
2021-12-31   25.000000 %

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

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Darwin
OS-release: 17.5.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.22.0
pytest: 3.5.0
pip: 10.0.0
setuptools: 39.0.1
Cython: None
numpy: 1.14.2
scipy: 1.0.1
pyarrow: None
xarray: None
IPython: 6.3.1
sphinx: None
patsy: None
dateutil: 2.7.2
pytz: 2018.4
blosc: None
bottleneck: None
tables: 3.4.2
numexpr: 2.6.4
feather: None
matplotlib: 2.2.2
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: 0.6.0
[

</details>
