add basic save and load

add menu
- save
- load
- demo on/off
- close + popup

#9 #10

save_pattern.hexpat

@@ -0,0 +1,22 @@
+struct Category {
+    float r,g,b,a;
+    char name[64];
+};
+
+struct Categorized_Day {
+    s32 year;
+    s32 month;
+    s32 day;
+    s32 category;
+};
+
+struct Calendar {
+    u32 version;
+    u32 num_categories;
+    u32 num_categorized_days;
+    
+    Category categories[num_categories];
+    Categorized_Day categorized_days[num_categorized_days];
+};
+
+Calendar calendar @ 0;