add sample plugin to go with the sample help (#2239)

plugins/CMakeLists.txt

@@ -106,6 +106,7 @@ if(BUILD_SUPPORTED)
     dfhack_plugin(command-prompt command-prompt.cpp)
     dfhack_plugin(confirm confirm.cpp LINK_LIBRARIES lua)
     dfhack_plugin(createitem createitem.cpp)
+    dfhack_plugin(cromulate cromulate.cpp)
     dfhack_plugin(cursecheck cursecheck.cpp)
     dfhack_plugin(cxxrandom cxxrandom.cpp LINK_LIBRARIES lua)
     dfhack_plugin(deramp deramp.cpp)

plugins/cromulate.cpp

@@ -0,0 +1,28 @@
+#include "Core.h"
+#include <Console.h>
+#include <Export.h>
+#include <PluginManager.h>
+
+using namespace DFHack;
+using namespace df::enums;
+
+DFHACK_PLUGIN("cromulate");
+
+command_result cromulate (color_ostream &out, std::vector <std::string> & parameters);
+
+DFhackCExport command_result plugin_init (color_ostream &out, std::vector <PluginCommand> &commands) {
+    commands.push_back(PluginCommand("cromulate",
+                                     "in-cpp plugin short desc", //to use one line in the ``[DFHack]# ls`` output
+                                     cromulate,
+                                     false,
+                                     "in-cpp plugin long help"));
+    return CR_OK;
+}
+
+DFhackCExport command_result plugin_shutdown (color_ostream &out) {
+    return CR_OK;
+}
+
+command_result cromulate (color_ostream &out, std::vector <std::string> &parameters) {
+    return CR_OK;
+}