ENH: Add type conversion to read_stata and StataReader
Added upcasting of numeric types which will default numeric data to either
int64 or float64.  This option has been enabled by default.

closes #8527

@jreback The big question remaining is the name: `preserve_dtypes=False` or `convert_dtypes=True`.

Also, the default behavior has changed, which might not be desirable (it has changed in the current PR so that it will convert to _preferred_ pandas types, e.g. any `float` to `float64` and any `int` to `int64`).
 I like `preserve_dtypes=True` (the default will need to be this for 0.15.1).
 @jreback Travis errored, but passes all tests  

I think it is ready if you don't see anything else.
 I restarted that job
ping me when green and can merge
 thanks 
