Resource fixes

1.  Can pass dshape and schema kwargs from Table to resource as in 

        Table('foo.csv', schema='...')

2.  resource('/path/to/*.csv') now enforces that the schema of the first item should be the same on all of the items.
In this exact case no, I think that should be usable.  This is strictly more robust that it was previously.  I also think that it is likely to fail sooner rather than later because we enforce a schema/dshape in the resource call rather than later on when people compute on things.