Tag releases based on <year>.<month>.<increment>

Move away from the week based increment because I don't use week numbers
for anything in my daily life, which makes them hard to evaluate time
from, and replace the per week bump with a global increment.  This means
that it's easy to see at a glance from two version numbers how far
appart they are in both time and number of releases.

tag-release.sh

@@ -1,11 +1,11 @@
 #!/bin/bash
 
-# Finds the next available r<year>.<week>.<bump> identifier for the current year and week
-YEAR_WEEK=$(date -u +%g.%-V)
-YEAR=${YEAR_WEEK:0:2}
-WEEK=${YEAR_WEEK:3}
-LAST_BUMP=$(git tag --list | grep '^r'$YEAR'\.'$WEEK'\.\(0\|[1-9][0-9]*\)$' | cut -d . -f 3 | sort -nr | head -n 1)
-RELEASE=r${YEAR_WEEK}.$(( ${LAST_BUMP:--1} + 1 ))
+# Finds the next available r<year>.<month>.<increment> identifier
+YEAR_MONTH=$(date -u +%Y.%-m)
+YEAR=${YEAR_MONTH:0:4}
+MONTH=${YEAR_MONTH:5}
+LAST_INCREMENT=$(git tag --list | grep '^r[1-9][0-9]*\.\([1-9]\|1[0-2]\)\.\(0\|[1-9][0-9]*\)$' | cut -d . -f 3 | sort -nr | head -n 1)
+RELEASE=r${YEAR_MONTH}.$(( ${LAST_INCREMENT:--1} + 1 ))
 
 git tag $RELEASE
 echo Tagged $RELEASE