port the make list functions and JWT, and expose the framework variables to hooks

lib/str.sh gains firstword, lastword, or, patsubst, filter, filter_out,
addprefix, addsuffix and jwt: what the catalogue .mk files are written in.
The make JWT macro split on the commas of its payload; this one does not.

lib/context.sh registers COMPOSE_PROJECT_NAME, APP, DOCKER_NETWORK_* and the
rest as lazy defaults, so a converted .mk keeps reading them as it did.

Hooks also load a directory-level _stack.env and _stack.sh, for the .mk files
of the catalogue that hold settings for several stacks at once.

lib/hooks.sh

@@ -2,6 +2,8 @@
 # hooks: the per-stack settings that used to live in a .mk file.
 #
 # A stack may ship, next to its compose files:
+#   _stack.env       settings shared by every stack of the directory
+#   _stack.sh        the same, computed
 #   <name>.env       dotenv, for plain values
 #   <name>.env.<env> the same, for one environment
 #   <name>.sh        shell, for values that have to be computed (fabio tags, JWTs)
@@ -14,10 +16,10 @@
 # myos_stack_hooks DIR NAME  load the hooks of one stack, most specific last
 myos_stack_hooks() {
   _hdir=$1; _hname=$2
-  for _h in "$_hdir/$_hname.env" "$_hdir/$_hname.env.$ENV"; do
+  for _h in "$_hdir/_stack.env" "$_hdir/$_hname.env" "$_hdir/$_hname.env.$ENV"; do
     [ -f "$_h" ] && myos_dotenv_load "$_h"
   done
-  for _h in "$_hdir/$_hname.sh" "$_hdir/$_hname.$ENV.sh"; do
+  for _h in "$_hdir/_stack.sh" "$_hdir/$_hname.sh" "$_hdir/$_hname.$ENV.sh"; do
     if [ -f "$_h" ]; then
       myos_debug "hook $_h"
       # shellcheck source=/dev/null