Hint: implement equality based on comparing string representations

This will work for "single package" hints, but should be extended to
consider "easy foo/1 bar/1" and "easy bar/1 foo/1" to be equivalent.

Signed-off-by: Adam D. Barratt <adam@adam-barratt.org.uk>

hints.py

@@ -65,6 +65,9 @@ class Hint:
     def __str__(self):
         return self._hint
 
+    def __eq__(self, other):
+        return str(self) == str(other)
+
     @property
     def type(self):
         return self._type