Goals:

1. DerValue be mostly immutable and used to read primitive values
2. DerInputStream be used to read constructed values
3. DerValue can be mutable for compatibility, but these calls are avoidable.
4. The major function of DerInputStream is itererating through sub-values. Except for getDerValue(), all other getXyz() calls should only be a wrapper of getDerValue().getXyz() and thus avoidable.
5. No more DerInputBuffer.

Success Metric:

1. Except for extreme cases (Ex: DerInputBuffer was called), all existing code should behave the same.
2. A new calling style that is simple, safe, and efficient.