feat(11.1-03): add the Architecture and Plugins docs sections

- architecture: introduction, Go modules and workspaces, application
  lifecycle, request lifecycle
- plugins: registration, scheduling, extending, testing
- verified Examples for backpack services, towel request context,
  pact schedules and festival events
- TestDocsRequiredPages lists the eight new pages

modules/towel/example_test.go

@@ -0,0 +1,37 @@
+package towel_test
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+
+	"git.golem15.com/golem15/summercms/modules/towel"
+)
+
+func ExampleWithLocale() {
+	// A middleware stores the organization once for the whole request.
+	withAcme := func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			ctx := towel.WithOrganization(r.Context(), "acme")
+			next.ServeHTTP(w, r.WithContext(ctx))
+		})
+	}
+
+	// The handler reads the values back from its request context.
+	listPosts := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		org, _ := towel.Organization(r.Context())
+		locale, ok := towel.Locale(r.Context())
+		if !ok {
+			locale = "en"
+		}
+		fmt.Fprintf(w, "posts for %s in %s", org, locale)
+	})
+
+	// surf sets the locale from Accept-Language; here the test sets it.
+	req := httptest.NewRequest(http.MethodGet, "/api/blog/posts", nil)
+	req = req.WithContext(towel.WithLocale(req.Context(), "pl"))
+	rec := httptest.NewRecorder()
+	withAcme(listPosts).ServeHTTP(rec, req)
+	fmt.Println(rec.Body.String())
+	// Output: posts for acme in pl
+}