read_csv  improvement
#### Code Sample, a copy-pastable example if possible

```python
df = pd.read_csv(f,sep='\t')

```
#### Problem description
Not so much a problem as a feature possibility - when reading without the encoding= parameter, the default can be made a bit smarter; since utf-16 seems to generally start with unique characters 0xFF 0xFE hex , if those chars start a file then it should be read as utf-16 (either after reading as utf-8 fails or as a first option) 
I am not so familiar with the pandas code and will try to implement this if someone can point me to where these changes would go - the  [pandas.io.parsers](https://github.com/pandas-dev/pandas/blob/master/pandas/io/parsers.py) is a bit opaque for me.
