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.

bin/myos

@@ -19,7 +19,7 @@ done
 MYOS_ROOT=$(cd "$(dirname "$_self")/.." && pwd -P)
 export MYOS_ROOT
 
-for _m in core str var tags naming stack config compose hooks; do
+for _m in core str var tags naming stack config compose hooks context; do
   # shellcheck source=/dev/null
   . "$MYOS_ROOT/lib/$_m.sh"
 done
@@ -225,6 +225,8 @@ fi
 # shellcheck disable=SC2086  # a list of references
 MYOS_STACKS=$(myos_group_expand $MYOS_REFS)
 
+myos_context_defaults
+
 # The uri a stack is served on: the tag helpers build on it, so it has to be
 # known before the hooks run.
 MYOS_SCOPE_FIRST=$(for _r in $MYOS_STACKS; do myos_scope "$_r"; break; done)