Hooks

- Implemented ::execute to run a command, feed it input, read it's output and
  return the exit status.

src/Hooks.h

@@ -45,6 +45,9 @@ public:
   void onAdd (Task&);
   void onModify (const Task&, Task&);
 
+private:
+  int execute (const std::string&, const std::string&, std::string&);
+
 private:
   std::vector <std::string> _scripts;
 };