Style guide: Use C99 style flexible arrays

Note that the function explicitly includes `void` in its parameter list to

indicate to the compiler that it takes no arguments.

### Zero-length arrays

Use zero-length arrays as the last member of a struct if the array needs to be

allocated in contiguous memory with its containing struct. For example:

### Contiguous memory structs

Use C99 flexible arrays as the last member of a struct if the array needs

to be allocated in contiguous memory with its containing struct.

A flexible array member is writen as array_name[] without a specific size.  

For example:

```

typedef struct {

  size_t length;

  uint8_t data[0];

  uint8_t data[];

} buffer_t;

// Allocate a buffer with 128 bytes available for my_buffer->data.