docs: add doxygen tags, configuration file, and autotooling

When ./configure --enable-doxygen is used one can browse internal api
documentation from docs/html directory.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

doc/.gitignore

@@ -0,0 +1,5 @@
+/Makefile
+/Makefile.in
+/doxy.conf
+/doxyfile.stamp
+/html

doc/Makefile.am

@@ -0,0 +1,18 @@
+EXTRA_DIST = doxy.conf.in introduction.dox
+
+if ENABLE_DOXYGEN
+
+doxyfile.stamp:
+	$(DOXYGEN) doxy.conf
+	date > doxyfile.stamp
+
+CLEANFILES = doxyfile.stamp
+
+all-local: doxyfile.stamp
+
+clean-local: clean-local-check
+.PHONY: clean-local-check
+clean-local-check:
+	-rm -rf html
+
+endif

doc/introduction.dox

@@ -0,0 +1,49 @@
+/*!
+@mainpage
+@section introduction Introduction
+
+This is dhcpd-pools ISC dhcp shared network and pool range usage
+analysis.  Purpose of command is to count usage ratio of each IP range
+and shared network pool which ISC dhcpd is in control of.  Users of the
+command are most likely ISPs and other organizations that have large IP
+space.
+
+Program is written C. Design goal is to get analysis done quickly where
+there is lots of data.  On cheap laptop the speed of analysis is roughly
+100k leases per second.  Number of ranges, or shared networks, does not
+make any significant difference in getting analysis done.
+
+@section main-copyright Copyright Policy
+
+The dhcpd-pools has BSD 2-clause license which also known as "Simplified
+BSD License" or "FreeBSD License".
+
+Copyright 2006- Sami Kerola. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+ 1. Redistributions of source code must retain the above copyright
+    notice, this list of conditions and the following disclaimer.
+ 2. Redistributions in binary form must reproduce the above copyright
+    notice, this list of conditions and the following disclaimer in the
+    documentation and/or other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR AND CONTRIBUTORS OR
+CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+The views and conclusions contained in the software and documentation are
+those of the authors and should not be interpreted as representing
+official policies, either expressed or implied, of Sami Kerola.
+
+*/