Class Annotations

This PR adds a notion of class annotations, within which the previous state variable annotations are nested.  This works though a new pragma with the following form:

```C++
#pragma cyclus note <dict>
```

Note decorations is used exactly like state variable decoration (antecedent must eval to a dict, must be from *within* a class declaration, etc) .  This is needed because as we move forward we may want introspectable class documentation, user levels, etc.