JVM specification for records

the current definition of the record attribute is:
```
Record {
         u2 attribute_name_index;
         u4 attribute_length;
         u2 components_count;
         component_info components[components_count];
     }
```

where component_info is:
```
    component_info {
         u2 name_index;
         u2 descriptor_index;
         u2 attributes_count;
         attribute_info attributes[attributes_count];
     }
```

If the component has a generic signature that is different from the erased descriptor, it is placed in a Signature attribute on the component, similarly as we do for field_info at present.