Add object attribute mechanism

This _kindof_ sucks.

This is my first idea of how to implement object attribute getters for
the object type.

Each type must provide an object-name-offset-type table, which gets
stored in the object v-table. The function `ws_object_attr_read()` allows
the _reading_ of such an attribute.

This code is untested by now and I consider this code as really ugly,
but I don't know a better way to do it by now. Please stay calm when
reviewing this.

Targets #64 
Nope, you read the type and either fail or set the value to the type read out.
You obviously might include the conversion functions in the table you now use for the size info.