maint: post-release administrivia

* NEWS: Add header line for next release.
* .prev-version: Record previous version.
* cfg.mk (old_NEWS_hash): Auto-update.

Signed-off-by: Simon Josefsson <simon@josefsson.org>
diff --git a/.prev-version b/.prev-version
index 43b5827..b30c4dc 100644
--- a/.prev-version
+++ b/.prev-version
@@ -1 +1 @@
-4.17.0
+4.18.0
diff --git a/NEWS b/NEWS
index bf7aa0f..6752f39 100644
--- a/NEWS
+++ b/NEWS
@@ -1,5 +1,8 @@
 GNU Libtasn1 NEWS                                     -*- outline -*-
 
+* Noteworthy changes in release ?.? (????-??-??) [?]
+
+
 * Noteworthy changes in release 4.18.0 (2021-11-09) [stable]
 - Improve GTK-DOC manual.  Closes: #35.
 - Improve --help and --version for tools with gnulib.  Closes: #37.
diff --git a/cfg.mk b/cfg.mk
index 2ce3162..24f2eef 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -18,7 +18,7 @@
 
 manual_title = Library for Abstract Syntax Notation One (ASN.1)
 
-old_NEWS_hash = d1ceb75ae4fc9ca56035419de91948d7
+old_NEWS_hash = 7552c904096db5eb5310051b1b7d8560
 
 bootstrap-tools = gnulib,autoconf,automake,libtoolize,make,makeinfo,bison,help2man,gtkdocize,tar,gzip