Merge branch 'trac3664' Add base LFC process code

This merge adds the basic code for handling lease file cleanup (LFC).
It provides the basic framework for the process as well as code to
do argument parsing.

doc/Doxyfile

@@ -650,6 +650,7 @@ INPUT                  = ../src/bin/d2 \
                          ../src/bin/dhcp6 \
                          ../src/bin/perfdhcp \
                          ../src/bin/sockcreator \
+                         ../src/bin/lfc \
                          ../src/hooks/dhcp/user_chk \
                          ../src/lib/asiolink \
                          ../src/lib/cc \