Passing reference parameters to get*Component functions doesn't work

Test case:

```
#include
fruit::Component getRootComponent(int& n) {
return fruit::createComponent().bindInstance(n);
}
static int n = 3;
int main() {
fruit::Injector injector(getRootComponent, n);
injector.get();
}
```

It should work, or at the very least it should fail with an error message mentioning this workaround:

```
#include
fruit::Component getRootComponent(int* n) {
return fruit::createComponent()
.bindInstance(n);
}
static int n = 3;
int main() {
fruit::Injector injector(getRootComponent, &n);
injector.get();
}
```