update README for Kea

This is mostly just a test of using new git repo for kea.
Point to developers website

Thsi is another test of git with new repo
[3391] Removed DNS specific folders from the tree.

Also, updated configure.ac to not reference removed files. The
--disable-dhcp and --disable-dns configuration flags have been removed.
[3391] Removed references to DNS docs in from doxygen.
[3391] Disable building lettuce tests.
[3391] Fix distcheck issues.
[3395] Updated BIND10 Guide, removing DNS parts and updating examples.
[3395] bind10-guide cleanup.
[3395] Comment out the preface.
[3391] Minor change to configure.ac as a result of the review.
[3158] Added doxygen developer's guide page for D2

Added src/bin/d2/images to image path in doc/Doxyfile
Added d2 subpage to doc/devel/mainpage.dox
Added the following:
[master] Merge branch 'trac3391'
[3394] Renamed Kea libraries from libb10-something to libkea-something.
[3395] Corrected a few grammatical miffs
[3395] Addressed review comments.
[master] Merge branch 'trac3395'
[3121] Moved validation logic to build method for TSIGKeyInfo parsing

Modified TSIGKeyInfoParser, TSIGKeyInfoListParser, and unit tests
[3158] Removed a few nits as result of the review.
[3158] Addressed review comments

Fixed the main page table of contents to include D2's sections as subpages
Minor word changes and clean up
[3394] Extraneous white space removed in dhcpsrv/Makefile.am