Move all core types into namespaces (#1886)

* Reorganize namespaces

- Most types are now moved into the `melonDS` namespace
- Only good chance to do this for a while, since a big refactor is next

* Fix the build

src/JitBlock.h

@@ -22,7 +22,7 @@
 #include "types.h"
 #include "TinyVector.h"
 
-namespace ARMJIT
+namespace melonDS
 {
 typedef void (*JitBlockEntry)();