restructure imageproxy package

- move binary from imageproxy.go to cmd/imageproxy/main.go
- move proxy package up to top level

proxy/cache.go

@@ -1,37 +0,0 @@
-// Copyright 2013 Google Inc. All rights reserved.
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package proxy
-
-// The Cache interface defines a cache for storing arbitrary data.  The
-// interface is designed to align with httpcache.Cache.
-type Cache interface {
-	// Get retrieves the cached data for the provided key.
-	Get(key string) (data []byte, ok bool)
-
-	// Set caches the provided data.
-	Set(key string, data []byte)
-
-	// Delete deletes the cached data at the specified key.
-	Delete(key string)
-}
-
-// NopCache provides a no-op cache implementation that doesn't actually cache anything.
-var NopCache = new(nopCache)
-
-type nopCache struct{}
-
-func (c nopCache) Get(string) ([]byte, bool) { return nil, false }
-func (c nopCache) Set(string, []byte)        {}
-func (c nopCache) Delete(string)             {}