Resource function for Stata dta files

Mostly because it was trivial to do thanks to Pandas

```Python
In [1]: from blaze import resource
res
In [2]: resource('examples/data/oil.dta')
Out[2]: 
    year  barrels
0   1880       30
1   1890       77
2   1900      149
3   1905      215
4   1910      328
5   1915      432
6   1920      689
7   1925     1069
8   1930     1412
9   1935     1655
10  1940     2150
11  1945     2595
12  1950     3803
13  1955     5626
14  1960     7674
15  1962     8882
16  1964    10310
17  1966    12016
18  1968    14104
19  1970    16690
20  1972    18584
21  1974    20389
22  1976    20188
23  1978    21922
24  1980    21722
25  1982    19411
26  1984    19837
27  1986    20246
28  1988    21338

In [3]: type(_)
Out[3]: pandas.core.frame.DataFrame
```