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/CRC32.cpp

@@ -20,6 +20,8 @@
 
 // http://www.codeproject.com/KB/recipes/crc32_large.aspx
 
+namespace melonDS
+{
 constexpr u32 _reflect(u32 refl, char ch)
 {
     u32 value = 0;
@@ -62,3 +64,5 @@ u32 CRC32(const u8 *data, int len, u32 start)
 
 	return (crc ^ 0xFFFFFFFF);
 }
+
+}