Update ChangeLog and bump version for v2.5.1 release

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

ChangeLog.md

@@ -3,13 +3,16 @@ ChangeLog
 
 All notable changes to the project are documented in this file.
 
-[v2.5.1][UNRELEASED]
+[v2.5.1][] - 2021-08-22
 -----------------------
 
-Minor build fixes, mostly related to older compilers pre-C99.
+### Changes
+- Add .sha256 checksum to dist files, useful for packagers
 
 ### Fixes
+- Fix #155: systemd Notify integration, restore `NotifyAccess=main`
 - Fix #165: ftbfs on older compilers, e.g. gcc 4.8.3, use -std=gnu99
+- Fix Documentation refs in systemd unit file, new man pages
 
 
 [v2.5.0][] - 2021-08-19
@@ -549,7 +552,7 @@ Initial public release by Carsten Schill.
 
 [mrdisc]: https://github.com/troglobit/mrdisc
 [RFC4286]: https://tools.ietf.org/html/rfc4286
-[UNRELEASED]: https://github.com/troglobit/smcroute/compare/2.5.0...HEAD
+[UNRELEASED]: https://github.com/troglobit/smcroute/compare/2.5.1...HEAD
 [v2.5.1]: https://github.com/troglobit/smcroute/compare/2.5.1...2.5.1
 [v2.5.0]: https://github.com/troglobit/smcroute/compare/2.4.4...2.5.0
 [v2.4.4]: https://github.com/troglobit/smcroute/compare/2.4.3...2.4.4

configure.ac

@@ -2,7 +2,7 @@
 # Process this file with autoconf to produce a configure script.
 
 AC_PREREQ(2.61)
-AC_INIT(SMCRoute, 2.5.1-beta1, https://github.com/troglobit/smcroute/issues, smcroute, https://troglobit.com/smcroute.html)
+AC_INIT(SMCRoute, 2.5.1, https://github.com/troglobit/smcroute/issues, smcroute, https://troglobit.com/smcroute.html)
 AC_CONFIG_AUX_DIR(aux)
 AM_INIT_AUTOMAKE([1.11 foreign])
 AM_SILENT_RULES([yes])