added osdialog example

projects/C/osdialog-example/src/main.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+#include "osdialog.h"
+
+int main(int argc, char const *argv[]) {
+  int res;
+
+  res = osdialog_message(OSDIALOG_INFO, OSDIALOG_OK, "Info こんにちは");
+  printf("Result: %d\n", res);
+
+  res = osdialog_message(OSDIALOG_WARNING, OSDIALOG_OK_CANCEL, "Warning こんにちは");
+  printf("Result: %d\n", res);
+
+  res = osdialog_message(OSDIALOG_ERROR, OSDIALOG_YES_NO, "Error こんにちは");
+  printf("Result: %d\n", res);
+
+  return 0;
+}

projects/C/osdialog-example/src/osdialog.c

@@ -0,0 +1 @@
+../third/osdialog/osdialog.c

projects/C/osdialog-example/src/osdialog_zenity.c

@@ -0,0 +1 @@
+../third/osdialog/osdialog_zenity.c