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/ROMList.cpp

@@ -18,6 +18,8 @@
 
 #include "ROMList.h"
 
+namespace melonDS
+{
 const ROMListEntry ROMList[] =
 {
 	{0x41464141, 0x00800000, 0x00000004},
@@ -6801,3 +6803,5 @@ const ROMListEntry ROMList[] =
 };
 
 const size_t ROMListEntryCount = sizeof(ROMList) / sizeof(ROMListEntry);
+
+}