Directory restructuring of object.h

Break object.h into constituent files.
Reduce number of #includes in other GC header files.
Introduce -inl.h files to avoid mirror files #include-ing each other.
Check invariants of verifier RegTypes for all constructors.

Change-Id: Iecf1171c02910ac152d52947330ef456df4043bc
diff --git a/src/oat.cc b/src/oat.cc
index 8032a11..b0a9aef 100644
--- a/src/oat.cc
+++ b/src/oat.cc
@@ -15,6 +15,7 @@
  */
 
 #include "oat.h"
+#include "utils.h"
 
 #include <zlib.h>