Assertions with cbor_assert(cond)

Hi,

I was wondering if there is a particular reason that the macro cbor_assert(cond) defined on line 64 in compilersupport_p.h is used instead of using a macro such as:

```c
# define MACRO do { if (!(cond)) return SomeCborError; } while (0)
```

The drawback of having an assertion from my point-of-view as someone who uses the library, is the fact that when the assertion fails, the program *crashes*. This is not ideal when I am fuzz testing my program since it will prevent me from knowing if it is my program that is causing the crash or the assertion from tinycbor.