Compiler warning in compile_time branch.

I'm seeing this warning from the compile_time branch:

```entityx\entityx/entityx.hh(240): warning C4267: 'argument': conversion from 'size_t' to 'uint32_t', possible loss of data```

Because
```
struct Components {
...
template
static void destroy(Storage &storage, const std::bitset &mask, std::size_t index) {
if (mask.test(component_index::value)) {
storage.template destroy(index);
}
}
```
The `Components.destroy` method takes size_t (and it looks like most of the storage classes use size_t), but the index of an Id is `uint32_t`. I'm compiling a 64bit executable, so I guess size_t is a uint64_t on my machine.