Start implementing HttpCamera.

This is a work in progress that does not yet support camera settings.

examples/httpcvstream/httpcvstream.cpp

@@ -0,0 +1,28 @@
+#include "cscore.h"
+#include "opencv2/core/core.hpp"
+
+#include <iostream>
+#include <stdio.h>
+
+int main() {
+  cs::HttpCamera camera{"httpcam", "http://localhost:8081/?action=stream"};
+  camera.SetVideoMode(cs::VideoMode::kMJPEG, 320, 240, 30);
+  cs::CvSink cvsink{"cvsink"};
+  cvsink.SetSource(camera);
+  cs::CvSource cvsource{"cvsource", cs::VideoMode::kMJPEG, 320, 240, 30};
+  cs::MjpegServer cvMjpegServer{"cvhttpserver", 8083};
+  cvMjpegServer.SetSource(cvsource);
+
+  cv::Mat test;
+  cv::Mat flip;
+  for (;;) {
+    uint64_t time = cvsink.GrabFrame(test);
+    if (time == 0) {
+      std::cout << "error: " << cvsink.GetError() << std::endl;
+      continue;
+    }
+    std::cout << "got frame at time " << time << " size " << test.size() << std::endl;
+    cv::flip(test, flip, 0);
+    cvsource.PutFrame(flip);
+  }
+}