Need syntax sugar for dataframe row selection
Current dataframe row selection  by columns is wordy ,  'rowsl()' method is need to make it looks simple. 

def _rowsl(df, selection_str):
   #syntax sugar to simplify column selection:
   #     df.rowsl('col_1>0.5 & col_2<40') act as 
   #     df[(df['col_1']>0.5) & (df['col_2']<40)]

```
#not_implement_yet
#rst = parsing_and_ filtering
return rst
```

DataFrame.rowsl = _rowsl
