Feature: Use arena-allocation for memory handling

Arena allocation make deallocation of nested structed MUCH faster, and
improves the spatial locality of allocations. It makes no sense to
deallocate only parts of a JSON structure so arenas are a good fit here.

include/util.h

@@ -10,6 +10,6 @@ __attribute__((__noreturn__)) void err_ctx(int exit_code, FILE* fp, const char*
 void* malloc_or_die(size_t size);
 void* realloc_or_die(void* ptr, size_t size);
 void* calloc_or_die(size_t nmemb, size_t size);
-void print_trace();
+void print_trace(void);
 
 #endif