Decompile jpegdecoder.c, padsetup.c and code_800C3C20.c (#217)

* Decompile jpegdecoder.c, padsetup.c and code_800C3C20.c

* change func_800C3C20's prototype and rename some fields in jpeg related structs

* Fix comment in Jpeg_GetU16 and change func_800C3C20

* use a switch in padsetup.c

src/code/code_800C3C20.c

@@ -0,0 +1,13 @@
+#include <global.h>
+
+u8 D_8012D200[] = {
+    0, 1, 2, 3, 4, 5, 6,
+};
+
+void func_800C3C20(void) {
+    s32 i;
+    
+    for (i = 0; i < ARRAY_COUNT(D_8012D200) & 0xFFFFFFFFu; i++) {
+        func_800F87A0(D_8012D200[i]);
+    }
+}