proposal: new sorting order for columns
when I want to sort one of the columns with a specific order, there is the only way to do this right now. example, we have this dataframe

``` python
import pandas as pd
df = pd.DataFrame({'good': [10], 'excellent': [20], 'bad': [10]})
df.head()
   bad  excellent  good
0  10   20         10  
```

and If I want to sort the columns with the `good excellent bad` order, there is the only way

``` py
pd.DataFrame(df, columns=['good', 'excellent', 'bad'])
   good  excellent  bad
0  10    20         10 
```

but this is ugly.

can you consider this way of solution?

``` py
import pandas as pd
df = pd.DataFrame({'good': [10], 'excellent': [20], 'bad': [10]})
df.sort_columns(specific_order=['good', excellent', 'bad'])
   good  excellent  bad
0  10    20         10 
```
