accessPolicy: Implement Put, Get, Delete access policy.

This patch implements Get,Put,Delete bucket policies

Supporting - http://docs.aws.amazon.com/AmazonS3/latest/dev/access-policy-language-overview.html

Currently supports following actions.

   "*":                             true,
   "s3:*":                          true,
   "s3:GetObject":                  true,
   "s3:ListBucket":                 true,
   "s3:PutObject":                  true,
   "s3:CreateBucket":               true,
   "s3:GetBucketLocation":          true,
   "s3:DeleteBucket":               true,
   "s3:DeleteObject":               true,
   "s3:AbortMultipartUpload":       true,
   "s3:ListBucketMultipartUploads": true,
   "s3:ListMultipartUploadParts":   true,

following conditions for "StringEquals" and "StringNotEquals"

   "s3:prefix", "s3:max-keys"

pkg/s3/access/README.md

@@ -0,0 +1,33 @@
+## Access Policy
+
+This package implements parsing and validating bucket access policies based on Access Policy Language specification - http://docs.aws.amazon.com/AmazonS3/latest/dev/access-policy-language-overview.html
+
+### Supports following effects.
+
+    Allow
+    Deny
+
+### Supports following set of operations.
+
+    *
+    s3:*
+    s3:GetObject
+    s3:ListBucket
+    s3:PutObject
+    s3:CreateBucket
+    s3:GetBucketLocation
+    s3:DeleteBucket
+    s3:DeleteObject
+    s3:AbortMultipartUpload
+    s3:ListBucketMultipartUploads
+    s3:ListMultipartUploadParts
+
+### Supports following conditions.
+
+    StringEquals
+    StringNotEquals
+
+Supported applicable condition keys for each conditions.
+
+    s3:prefix
+    s3:max-keys