autotools: versionning consistent with CMake

configure.ac

-AC_INIT(opendht, 0.6.2)
+dnl define macros
+m4_define([opendht_major_version], 0)
+m4_define([opendht_minor_version], 6)
+m4_define([opendht_patch_version], 2)
+m4_define([opendht_version],
+		  [opendht_major_version.opendht_minor_version.opendht_patch_version])
+
+AC_INIT(opendht, [opendht_version])
 AC_CONFIG_AUX_DIR(ac)
 AM_INIT_AUTOMAKE([foreign subdir-objects])
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CANONICAL_HOST
 
+AC_SUBST(OPENDHT_MAJOR_VERSION, opendht_major_version)
+AC_SUBST(OPENDHT_MINOR_VERSION, opendht_minor_version)
+AC_SUBST(OPENDHT_PATCH_VERSION, opendht_patch_version)
+
 AC_ARG_ENABLE([debug], AS_HELP_STRING([--enable-debug], [Build in debug mode, adds stricter warnings, disables optimization]))
 AS_IF([test "x$enable_debug" = "xyes"],
       [CXXFLAGS="${CXXFLAGS} -g -Wno-return-type -Wall -Wextra -Wnon-virtual-dtor -O0"],

src/Makefile.am

@@ -3,7 +3,7 @@ SUBDIRS = argon2
 lib_LTLIBRARIES = libopendht.la
 
 AM_CPPFLAGS = -I../include/opendht
-libopendht_la_LDFLAGS = @LDFLAGS@ @GnuTLS_LIBS@ @Nettle_LIBS@
+libopendht_la_LDFLAGS = @LDFLAGS@ @GnuTLS_LIBS@ @Nettle_LIBS@ -version-number @OPENDHT_MAJOR_VERSION@:@OPENDHT_MINOR_VERSION@:@OPENDHT_PATCH_VERSION@
 libopendht_la_LIBADD = ./argon2/libargon2.la
 
 libopendht_la_SOURCES = \