feat: introduce support for plugins

internal/examples/plugins/main.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	_ "embed"
+	"net/http"
+
+	"github.com/go-via/via"
+	"github.com/go-via/via/h"
+)
+
+// In this example we create a Via application with a plugin that adds PicoCSS. The plugin
+// is handed to Via in the app Configuration.
+
+//go:embed pico.yellow.min.css
+var picoCSSFile []byte
+
+func main() {
+	v := via.New()
+	v.Config(via.Options{
+		DocumentTitle: "Via With PicoCSS Plugin",
+		Plugins:       []via.Plugin{PicoCSSPlugin},
+	})
+
+	v.Page("/", func(c *via.Context) {
+		c.View(func() h.H {
+			return h.Section(h.Class("container"),
+
+				h.H1(h.Text("Hello from ⚡Via")),
+				h.Div(h.Class("grid"),
+					h.Button(h.Text("Primary")),
+					h.Button(h.Class("secondary"), h.Text("Secondary")),
+				),
+			)
+		})
+	})
+	v.Start(":3000")
+}
+
+func PicoCSSPlugin(v *via.V) {
+	v.HandleFunc("GET /_plugins/picocss/assets/style.css", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "text/css")
+		_, _ = w.Write(picoCSSFile)
+	})
+	v.Config(via.Options{
+		DocumentHeadIncludes: []h.H{
+			h.Link(h.Rel("stylesheet"), h.Href("/_plugins/picocss/assets/style.css")),
+		},
+	})
+}