Allowing DataFrameGroupBy as input

[jingmin1987]

Hi,

I found out that the current implementation only takes DataFrame but not DataFrameGroupBy which is commonly used when processing information on multiple tickers in one go. I made a quick update to allow such and would like to know if you'd like to incorporate this feature.

Example dataframe to process:

To compute SMA for all tickers using current implementation:

df_all = []
for _, group in df.groupby(level=0):
    df_all.append(TA.SMA(group))

df['SMA'] = pd.concat(df_all)

To compute SMA for all tickers using proposed implementation:

df['SMA'] = TA.SMA(df.groupby(level=0))

You can take a look at the implementation detail at
master...jingmin1987:master