Implement nested validations.

This allows a list of validations to contain a dictionary of yet
more validations in order to accomodate writing validations
for nested dictionaries.

tests/test_validator.py

@@ -221,3 +221,40 @@ def test_conditional_validator(self):
         }
         assert validate(passes, test_case)[0]
         assert not validate(fails, test_case)[0]
+
+    def test_nested_validations(self):
+        passes = {
+            "foo": [Required, Equals(1)],
+            "bar": [
+                Required, 
+                {
+                    "baz": [Required, Equals(2)],
+                    "qux": [Required, {
+                        "quux": [Required, Equals(3)]
+                    }]
+                }
+            ]
+        }
+        fails = {
+            "foo": [Required, Equals(2)],
+            "bar": [
+                Required, 
+                {
+                    "baz": [Required, Equals(3)],
+                    "qux": [Required, {
+                        "quux": [Required, Equals(4)]
+                    }]
+                }
+            ]
+        }
+        test_case = {
+            "foo": 1,
+            "bar": {
+                "baz": 2,
+                "qux": {
+                    "quux": 3
+                }
+            }
+        }
+        assert validate(passes, test_case)[0]
+        assert not validate(fails, test_case)[0]

validator/__init__.py

@@ -361,7 +361,16 @@ def validate(validation, dictionary):
                 errors[key] = "must be present"
                 continue
         for v in validation[key]:
-            # skip Required, since it was already
+            # Ok, need to deal with nested
+            # validations.
+            if isinstance(v, dict):
+                valid, nested_errors = validate(v, dictionary[key])
+                if nested_errors:
+                    errors[key].append(nested_errors)
+                continue
+            # Done with that, on to the actual
+            # validating bit.
+            # Skip Required, since it was already
             # handled before this point.
             if not v == Required:
                 # special handling for the