update to version 1.4.0

* improved Doxygen documentation
* cmake: add support to build documentation
* cmake: improve build on macOS
* API change: storage policies, getPublicAddress now use SockAddr
* NodeExport: added msgpack serialization
* fixed issue that could cause occasional request failures
* minor bug fixes
* minor performance improvements

CMakeLists.txt

 cmake_minimum_required (VERSION 3.1)
 project (opendht)
 set (opendht_VERSION_MAJOR 1)
-set (opendht_VERSION_MINOR 3.6)
+set (opendht_VERSION_MINOR 4.0)
 set (opendht_VERSION ${opendht_VERSION_MAJOR}.${opendht_VERSION_MINOR})
 set (PACKAGE_VERSION ${opendht_VERSION})
 set (VERSION "${opendht_VERSION}")

configure.ac

 dnl define macros
 m4_define([opendht_major_version], 1)
-m4_define([opendht_minor_version], 3)
-m4_define([opendht_patch_version], 6)
+m4_define([opendht_minor_version], 4)
+m4_define([opendht_patch_version], 0)
 m4_define([opendht_version],
 		  [opendht_major_version.opendht_minor_version.opendht_patch_version])