Change api error structure

include/siadrive_api/siacommon.h

@@ -98,6 +98,36 @@ get_access:\
 set_access:\
 	type Set##name(const type& value) { json_doc[#name] = value; return value; }
 
+template<typename T>
+class CSiaError
+{
+public:
+  CSiaError()
+  {
+    SetCode(T::Success);
+  }
+
+  CSiaError(const T& t)
+  {
+    SetCode(t);
+  }
+
+  CSiaError(const T& code, const SString& reason)
+  {
+    SetCode(code);
+    SetReason(reason);
+  }
+
+public:
+  Property(T, Code, public, private)
+    Property(SString, Reason, public, private)
+
+public:
+  operator bool() { return GetCode() == T::Success; }
+  operator bool() const { return GetCode() == T::Success; }
+  CSiaError& operator=(const T& code) { SetCode(code); return *this; }
+};
+
 typedef struct 
 {
 	SString HostName;
@@ -107,7 +137,7 @@ typedef struct
 
 template<typename T>
 inline bool ApiSuccess(const T& t) {
-	return t == T::Success;
+  return static_cast<bool>(t);
 }
 
 typedef ttmath::UInt<256> Hastings;