4.4.0 Introduces several variations on building with Bind9 which need to be documented:

1. Create a new doxygen file: dhcp/doc/devel/building.dox, following
patterns established by similiar files such as atf.doc, to document
the relevant build options and procedures

2. Modify mainpage.dox to add the new file as a subsection

3. Add a reference to this file in the README under the "BUILDING IT"
section. There is currently a similiar entry for the ATF section.

4. Add a brief description on how to build the developer's guid to the
README file.