Don't merge RRs in the incoming packets

- misleading statement
- module name in heading
- s/forward\./example./g

Query plan modules + synthetic PTR/A/AAAA records

close #166

Gcov

This MR adds support to enable code coverage testing with:

```shell
./configure --enable-code-coverage
make
make check-code-coverage
```

The output can be found in $(PACKAGE_NAME)-$(PACKAGE_VERSION)-coverage directory.

You have to have lcov package installed for this to work.

DNSKEY in non-apex nodes

This changeset improves handling of DNSKEY records in non-apex nodes.