Fixing return types.

When plcrash_async_read_addr() was removed in commit 1eb3c7b, the call
sites were not updated properly. plcrash_async_task_memcpy() returns
plcrash_error_t and not kern_return_t.

Issue: PLCR-543
Removing leading whitespace.

Issue: PLCR-543
Documenting the special handling of v1 reports.

Issue: PLCR-543
Narrowing the scope of diagnostic ignore pragmas.

Issue: PLCR-543
Ensure that a code type is always set.

This is currently impossible to reach, but if more processor info encodings are added this code will have something to fall back onto.

Issue: PLCR-543