Type aware PAIR macro

Currently we have macros such as SHIVA_T_PAIR_RCX(varname) which are implemented like:

```
#define SHIVA_T_PAIR_RCX(var) register int64_t var asm("rcx");
```

But should be something like

```
#define SHIVA_T_PAIR_RCX(type, var) register type var asm("rcx");
```

Therefore we can simply specify the type, otherwise it uses int64_t and we have
to use casting in the code to get our type.
 
