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.

spec/unit/str_spec.sh

@@ -68,3 +68,55 @@ Describe 'lib/str.sh'
     End
   End
 End
+
+# The make list functions the catalogue relies on, ported so that a stack hook
+# reads like the .mk it replaces.
+Describe 'lib/str.sh list functions'
+  It 'takes the first and last word'
+    When call myos_firstword "a b c"
+    The output should equal "a"
+  End
+  It 'takes the last word'
+    When call myos_lastword "a b c"
+    The output should equal "c"
+  End
+  It 'returns the first argument that is not empty'
+    When call myos_or "" "" "third"
+    The output should equal "third"
+  End
+  Describe 'myos_patsubst'
+    Parameters
+      "%"      "pre%"     "a b"        "prea preb"
+      "%.yml"  "%.yaml"   "a.yml b.md" "a.yaml b.md"
+      "%"      "%/"       "x y"        "x/ y/"
+    End
+    It "substitutes $1 -> $2 in $3"
+      When call myos_patsubst "$1" "$2" "$3"
+      The output should equal "$4"
+    End
+  End
+  It 'filters a list'
+    When call myos_filter "a%" "abc bcd axe"
+    The output should equal "abc axe"
+  End
+  It 'filters a list out'
+    When call myos_filter_out "local master main" "staging"
+    The output should equal "staging"
+  End
+  It 'drops the words it is told to'
+    When call myos_filter_out "local master main" "master"
+    The output should equal ""
+  End
+  It 'adds a prefix and a suffix'
+    When call myos_addprefix "x." "a b"
+    The output should equal "x.a x.b"
+  End
+End
+
+Describe 'lib/str.sh myos_jwt'
+  It 'signs a token whose payload decodes back'
+    When call myos_jwt "" '{"role":"anon"}' secret
+    The output should start with "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9."
+    The output should include "eyJyb2xlIjoiYW5vbiJ9"
+  End
+End