Caching policies added.

We used httpcache library to implement this. As it was not possible to support different policies, I mostly copied and modified it.

cache/diskcache/diskcache_test.go

@@ -0,0 +1,18 @@
+package diskcache
+
+import (
+	"github.com/geziyor/geziyor/cache"
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestDiskCache(t *testing.T) {
+	tempDir, err := ioutil.TempDir("", "cache")
+	if err != nil {
+		t.Fatalf("TempDir: %v", err)
+	}
+	defer os.RemoveAll(tempDir)
+
+	cache.PleaseCache(t, New(tempDir))
+}