Implemented Higher Half Kernel!

- Minor makefile chnages
- stage3.c "prekernel", sets up memory stuff and jumps to kernel
- kernel is now at 0xC0000000 - 3GB+ "higher half"
- Added some global variables in memory/addresses.h

src/stage3.ld

@@ -0,0 +1,16 @@
+/* Third stage "prekernel" */
+SECTIONS {
+    .text 0x50000 : {
+        *(entry);
+        *(.text*);
+    }
+    .data : {
+        *(.data*);
+    }
+    .rodata : {
+        *(.rodata*);
+    }
+    .bss : {
+        *(.bss*);
+    }
+}