partial cleanup of the macro pkg and move it from /core/router to the root because it may be used by the end-developers now to ammend the available macros per application

Former-commit-id: 951a5e7a401af25ecaa904ff6463b0def2c87afb

macro/handler/handler.go

@@ -0,0 +1,52 @@
+// Package handler is the highest level module of the macro package which makes use the rest of the macro package,
+// it is mainly used, internally, by the router package.
+package handler
+
+import (
+	"github.com/kataras/iris/context"
+	"github.com/kataras/iris/macro"
+)
+
+// MakeHandler creates and returns a handler from a macro template, the handler evaluates each of the parameters if necessary at all.
+// If the template does not contain any dynamic attributes and a special handler is NOT required
+// then it returns a nil handler and false as its second output value,
+// the caller should check those two values before any further action.
+func MakeHandler(tmpl *macro.Template) (context.Handler, bool) {
+	needsMacroHandler := len(tmpl.Params) > 0
+	if !needsMacroHandler {
+		return nil, false
+	}
+
+	// check if we have params like: {name:string} or {name} or {anything:path} without else keyword or any functions used inside these params.
+	// 1. if we don't have, then we don't need to add a handler before the main route's handler (as I said, no performance if macro is not really used)
+	// 2. if we don't have any named params then we don't need a handler too.
+	for _, p := range tmpl.Params {
+		if p.CanEval() {
+			// if at least one needs it, then create the handler.
+			needsMacroHandler = true
+			break
+		}
+	}
+
+	if !needsMacroHandler {
+		return nil, false
+	}
+
+	handler := func(ctx context.Context) {
+		for _, p := range tmpl.Params {
+			if !p.CanEval() {
+				continue // allow.
+			}
+
+			if !p.Eval(ctx.Params().Get(p.Name), ctx.Params()) {
+				ctx.StatusCode(p.ErrCode)
+				ctx.StopExecution()
+				return
+			}
+		}
+		// if all passed, just continue.
+		ctx.Next()
+	}
+
+	return handler, true
+}