Added Caching Module

The Caching Module Caches the images that have been extracted and for
persistence writes the images to a cache file.

In the cache file the data is stored by tab separated values

        `%s\t%s\t%s`

the cache is first loaded in the memory ( CACHE_LIST ) during the start of application
and then extracted images are added to the map CACHE_LIST which is
writtern to the cache file before exiting the program.

cache/cache_test.go

@@ -0,0 +1,16 @@
+package cache
+
+import "testing"
+
+func TestLoadCache(t *testing.T) {
+	expectedResult := [2]string{"hello/wer.jpg", "hello/iwer.jpg"}
+	loadCache("./testdata/cache.txt")
+	var i int = 0
+	for _, v := range CACHE_LIST {
+		if v != expectedResult[i] {
+			if v != expectedResult[i+1] {
+				t.Errorf("Didn't Get The Expected Value receieved %s", v)
+			}
+		}
+	}
+}