Option to return pandas DataFrame from TableSet or ColumnSet

[edwinhu]

Currently TabletSets and ColumnSets are represented as "tablified" PrettyTables. However when working with a database with lots of tables, or a table with lots of columns (>100) it would be nice to be able to return only a slice of the table.

An easy way to do this would be to have the option to return the TableSets or ColumnSets as pandas DataFrames.

Obviously the pandas DataFrame representation in the IPython terminal is not as pretty, but at least in IPython notebook the HTML representation of DataFrames is quite nice.

Something like:

rows = []
for col in self._columns:
    rows += [{"Column":col.name, "Type":col.type, "Foreign Keys":col._str_foreign_keys(), "Reference Keys":col._str_ref_keys()}]    
df = pd.DataFrame(li)    

Perhaps in a _repr_df_ function.