Specification clarifications

[ved-rivos]

Clarifications and suggestions from David Kruckemeyer:

1. Clarify the severity of information errors.
2. Section 2.4.1 Reword "overwrites" to "updates any field of" in description of rdip clearing.
3. Clarify that already asserted signals are unaffected by clearing else to 0
4. Add guidance for class/priority specific SW handlers and SW guidance on reconfiguration of signals
5. Clarify it is the first overflow, i.e. the one that sets the ceco bit, that leads to the signal being generated.
6. Section 2.5: Clarify that statement "new error is recorded" includes writes and overwrites.

[ved-rivos]

These clarifications and suggestions were included in PR #49