Support for standard containers

The serialization and deserialization of containers is handled as follows:

std::map<std::string, ...>, std::unordered_map<std::string, ...>, maps with any numeric types (integral and floating points) as keys, and any objects where the ReflectionType is either a std::string or a numeric type are treated as objects.

Consider the following map:

std::map<std::string, std::string> homer;
homer["firstName"] = "Homer";
homer["lastName"] = "Simpson";

This will be represented as follows:

{"firstName":"Homer","lastName":"Simpson"}

The same is true for numeric types:

std::map<int, std::string> homer;
homer[1] = "Homer";
homer[2] = "Simpson";

This will be represented as follows:

{"1":"Homer","2":"Simpson"}

If you wrap your keys into a rfl::Validator, this will be treated as an object as well:

using Between1and3 = rfl::Validator<int, rfl::Minimum<1>, rfl::Maximum<3>>;
std::map<Between1and3, std::string> homer;
homer[1] = "Homer";
homer[2] = "Simpson";

This will also be represented as follows:

{"1":"Homer","2":"Simpson"}

All other supported standard containers (other than std::variant, std::optional, std::unique_ptr and std::shared_ptr) will be represented as arrays. Containers for which the value_type is a key-value-pair will be represented as arrays of pairs.