Dynamic library module is now only a thin wrapper that loads dynamic
libraries and forwards all function calls directly to the loaded module.
This meant adding get_mem and clear, and get_mem calls have been added
in the expected places.

Documentation has also been added to the example.conf and the
unbound.conf manpage.

Allows the use of multiple dynamic modules. Simply add more "dynlib"
entries to the "modules-config" and the same amount of "dynlib-file"
entries in the dynlib configuration block.

This adds the possibility to properly register inplace callbacks in the
dynamic library module. It works by creating a wrapper procedure that
is available to the dynamic library and will call the given callback
through a whitelisted callback function.

The dynamic library example has already been improved to include
comments and some simple examples on allocating and deallocating memory
and registering callbacks.

This adds the "dynlib: " prefix to all messages created by the
`helloworld.c` dynamic library example.

It also adds logging of queries that pass through `operate`.

The return code of the init procedure was just set to be 1 in the
dynamic library loading module. This ha been rectified and it will now
return whatever is returned from the loaded module.