Add CTR encryption.

- Added ContentEncAESSettings, AESSettingsCipherMode,
  AESSettingsCipherInitData elements to the parser and muxer.
- Changed ParseContentEncodingsEntry, ParseContentEncodingEntry,
  and ParseEncryptionEntry to use PasreElementHeader.
- Added ParseContentEncAESSettingsEntry function.
- PS6 removed AESSettingsCipherInitData.
- PS9 Addressed comments, Fixed some LINT issues, and converted
  mkvwriter.h/.cpp to Unix line endings.
- PS10 Addressed comments.

Change-Id: I9d96a0c194f74a6c9bf0001aa0286196e410f07e

webmids.hpp

@@ -1,4 +1,4 @@
-// Copyright (c) 2011 The WebM project authors. All Rights Reserved.
+// Copyright (c) 2012 The WebM project authors. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the LICENSE file in the root of the source
@@ -101,6 +101,9 @@ enum MkvId {
   kMkvContentEncryption       = 0x5035,
   kMkvContentEncAlgo          = 0x47E1,
   kMkvContentEncKeyID         = 0x47E2,
+  kMkvContentEncAESSettings   = 0x47E7,
+  kMkvAESSettingsCipherMode   = 0x47E8,
+  kMkvAESSettingsCipherInitData = 0x47E9,
   //end ContentEncodings
   //Cueing Data
   kMkvCues                    = 0x1C53BB6B,