API/DOC: status of low_memory kwarg of read_csv/table
I am getting the following warning:

```
/usr/local/lib/python2.7/dist-packages/pandas-0.13.0rc1_78_g142ca62-py2.7-linux-x86_64.egg/pandas/io/parsers.py:1050: 
DtypeWarning: Columns (6) have mixed types. Specify dtype option on import or set low_memory=False.
  data = self._reader.read(nrows)
```

but I can find no documentation for `low_memory`
