io.rst needs updating to reflect api sql API methods introduced in 0.13
@mangecoeur noted in https://github.com/pydata/pandas/issues/4163#issuecomment-32272752

```
http://pandas.pydata.org/pandas-docs/stable/io.html#sql-queries
Also needs updating since it doesn't reflect the updated API 
(that was already introduced in 0.13 I think) which uses read_sql 
and to_sql for consistency with e.g. the CSV api.
```
