logd: add a SerializedLogBuffer suitable for compression

Initial commit for a SerializedLogBuffer.  The intention here is for
the serialized data to be compressed (currently using zlib) to allow
for substantially longer logs in the same memory footprint.

Test: unit tests
Change-Id: I2528e4e1ff1cf3bc91130173a107f371f04d911a
diff --git a/logd/main.cpp b/logd/main.cpp
index 773ffb8..46b6567 100644
--- a/logd/main.cpp
+++ b/logd/main.cpp
@@ -58,6 +58,7 @@
 #include "LogStatistics.h"
 #include "LogTags.h"
 #include "LogUtils.h"
+#include "SerializedLogBuffer.h"
 #include "SimpleLogBuffer.h"
 
 #define KMSG_PRIORITY(PRI)                                 \