expose values with getattr

[ekorman]

this PR does the following to address #571:

• for attributes of a StaticCollection that are simple types (e.g. String, Integer, etc), have __getattribute__ return the value
• update __repr__ to be explicit that these objects are not standard types. this is something that made me confused when i was using valor because it made me think that certain objects such as String, Integer were built-in types

[ntlind]

#571