cipd: Refactor client to make it more readable.

go/src/infra/tools/cipd/doc.go

-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-/*
-Package cipd implements client side of Chrome Infra Package Deployer.
-
-TODO: write more.
-
-Binary package file format (in free form representation):
-  <binary package> := <zipped data>
-  <zipped data> := DeterministicZip(<all input files> + <manifest json>)
-  <manifest json> := File{
-    name: ".cipdpkg/manifest.json",
-    data: JSON({
-      "FormatVersion": "1",
-      "PackageName": <name of the package>
-    }),
-  }
-  DeterministicZip = zip archive with deterministic ordering of files and stripped timestamps
-
-Main package data (<zipped data> above) is deterministic, meaning its content
-depends only on inputs used to built it (byte to byte): contents and names of
-all files added to the package (plus 'executable' file mode bit) and a package
-name (and all other data in the manifest).
-
-Binary package data MUST NOT depend on a timestamp, hostname of machine that
-built it, revision of the source code it was built from, etc. All that
-information will be distributed as a separate metadata packet associated with
-the package when it gets uploaded to the server.
-
-TODO: expand more when there's server-side package data model (labels
-and stuff).
-*/
-package cipd
-
-import "github.com/Sirupsen/logrus"
-
-// Default package level logger.
-var log = logrus.New()