[WIP] Test table coverage

I've added a few tests just so you guys can see my progress. I hope to have it fully tested today or tomorrow.
I don't agree with this test.  While it's currently valid I don't think that it represents preferable behavior.  

I suggest adding the following code to the `Expr` class

```Python
+    @property
+    def shape(self):
+        return datashape.to_numpy(self.dshape)[0]
+
+    @property
+    def dtype(self):
+        return datashape.to_numpy_dtype(self.schema)
+
+    @property
+    def schema(self):
+        return dshape(self.dshape[-1])
```