Mass file extension update.

- Use .cc and .h everywhere.
- Update includes/include guards.
- Remove extra makefile targets necessitated by previous mix
  of cpp/cc.

Change-Id: I7aad29152d4177937f8f42927c16c6572228c104
diff --git a/vttdemux.cc b/vttdemux.cc
index 96267d0..5885e9e 100644
--- a/vttdemux.cc
+++ b/vttdemux.cc
@@ -14,8 +14,8 @@
 #include <string>
 #include <utility>
 
-#include "mkvparser/mkvparser.hpp"
-#include "mkvparser/mkvreader.hpp"
+#include "mkvparser/mkvparser.h"
+#include "mkvparser/mkvreader.h"
 #include "webvtt/webvttparser.h"
 
 #ifdef _MSC_VER