ENH: Include TALib output names in ta transform results.

For TALib functions like MACD that have output names, return a
DataFrame that for which the columns are the output names of the
function.

So that when using a TALib function, the algorithm doesn't need
to know the index position of the desired result, in favor of using
the name of the result.

e.g.

```
macd_result['AAPL'][0]
```

becomes,
```
macd_result['AAPL']['macd']
```

and
```
macd_result['AAPL'][1]
```

becomes,
```
macd_result['AAPL']['macdsignal']
```

Also, change return type of functions that return floats from a
dictionary to a Series, so that the function is always returning a
pandas type.