Created non-templated base classes

[eidheim]

The base class is no longer a template class, making HTTP/HTTPS independent polymorphism on the client/server classes possible.

At first I didn't much like the idea due to added complexity, but now I'm pretty comfortable with the changes since the final solution is somewhat clean if not cleaner than before. Feedback is required though.

Related to issue #168. See also discussion on PR #208.

Example use:

#include "client_https.hpp"
#include "server_https.hpp"
#include <vector>

int main() {
  auto io_service = std::make_shared<SimpleWeb::asio::io_service>();
  std::vector<std::unique_ptr<SimpleWeb::ServerBase>> servers;

  servers.emplace_back(new SimpleWeb::Server<SimpleWeb::HTTP>());
  servers.back()->io_service = io_service;
  servers.back()->config.port = 8080;
  servers.back()->default_resource["GET"] = [](std::shared_ptr<SimpleWeb::Server<>::Response> response,
                                               std::shared_ptr<SimpleWeb::Server<>::Request> /*request*/) {
    response->write("Hello World");
  };

  servers.emplace_back(new SimpleWeb::Server<SimpleWeb::HTTPS>("server.crt", "server.key"));
  servers.back()->io_service = io_service;
  servers.back()->config.port = 8081;
  servers.back()->default_resource["GET"] = servers[0]->default_resource["GET"];

  for(auto &server : servers)
    server->start();

  io_service->run();
}