examples : add "simple-rx" example + minor clean-up

examples/simple-rx/main.cpp

@@ -0,0 +1,30 @@
+#include "ggwave/ggwave.h"
+
+#include "ggwave-common.h"
+#include "ggwave-common-sdl2.h"
+
+#include <cstdio>
+#include <thread>
+
+int main(int argc, char** argv) {
+    printf("Usage: %s [-cN]\n", argv[0]);
+    printf("    -cN - select capture device N\n");
+    printf("\n");
+
+    auto argm = parseCmdArguments(argc, argv);
+    int captureId = argm["c"].empty() ? 0 : std::stoi(argm["c"]);
+
+    if (GGWave_init(0, captureId) == false) {
+        fprintf(stderr, "Failed to initialize GGWave\n");
+        return -1;
+    }
+
+    while (true) {
+        std::this_thread::sleep_for(std::chrono::milliseconds(1));
+        GGWave_mainLoop();
+    }
+
+    GGWave_deinit();
+
+    return 0;
+}