Improve heading levels

blog/post/2016-05-28-catching-exceptions.md

@@ -328,7 +328,7 @@ The method does not need to modify the IDT, so it takes `self` by immutable refe
 
 Then we pass a pointer to our `ptr` structure to the `lidt` function, which calls the `lidt` assembly instruction in order to reload the IDT register. We need an unsafe block here, because the `lidt` assumes that the specified handler addresses are valid.
 
-### Safety
+#### Safety
 But can we really guarantee that handler addresses are always valid? Let's see:
 
 - The `Idt::new` function creates a new table populated with non-present entries. There's no way to set these entries to present from outside of this module, so this function is fine.
@@ -361,7 +361,7 @@ Well, we construct an IDT _on the stack_ and load it. It is perfectly valid unti
 
 Now imagine that the `cause_page_fault` function declared an array of pointers instead. If the present was coincidentally set, the CPU would jump to some random pointer and interpret random memory as code. This would be a clear violation of memory safety.
 
-### Fixing the load method
+#### Fixing the load method
 So how do we fix it? We could make the load function itself `unsafe` and push the unsafety to the caller. However, there is a much better solution in this case. In order to see it, we formulate the requirement for the `load` method:
 
 > The referenced IDT must be valid until a new IDT is loaded.
@@ -432,7 +432,7 @@ error: references in statics may only refer to immutable values [E0017]
 ```
 The reason is that the Rust compiler is not able to evaluate the value of the `static` at compile time. Maybe it will work someday when `const` functions become more powerful. But until then, we have to find another solution.
 
-### Lazy Statics to the Rescue
+#### Lazy Statics to the Rescue
 Fortunately the `lazy_static` macro exists. Instead of evaluating a `static` at compile time, the macro performs the initialization when the `static` is referenced the first time. Thus, we can do almost everything in the initialization block and are even able to read runtime values.
 
 With `lazy_static`, we can define our IDT without problems:
@@ -552,7 +552,7 @@ pub extern "C" fn rust_main(...) {
 ```
 Now the output ends on the `guard page` line. No `EXCEPTION` message and no `It did not crash` message either. What's happening?
 
-### Debugging
+#### Debugging
 Let's debug it using [GDB]. It is a console debugger and works with nearly everything, including QEMU. To make QEMU listen for a debugger connection, we start it with the `-s` flag:
 
 [GDB]: https://www.gnu.org/software/gdb/