Implement DataFrame.sort for axis=1
Am I missing something here?

```
import numpy as np
import pandas

x = np.array([[0,2,4],[2,0,7],[4,7,0]])
df = pandas.DataFrame(x, index=["a","b", "c"], columns=["a","b","c"])
df.sort("b", inplace=True)
#raises error for axis=1
#df.sort("c", axis=1, inplace=True)
# same with sort_index

# desired result
df.sort("b").T.sort("c").T
```
