Move DBusException and wrapErrors to separate module

Also improved its implemention.
This prepares for new exception types to be added in later commits.

source/ddbus/exception.d

@@ -0,0 +1,37 @@
+module ddbus.exception;
+
+import ddbus.c_lib;
+
+package T wrapErrors(T)(
+  T delegate(DBusError *err) del,
+  string file = __FILE__,
+  size_t line = __LINE__,
+  Throwable next = null
+) {
+  DBusError error;
+  dbus_error_init(&error);
+  T ret = del(&error);
+  if(dbus_error_is_set(&error)) {
+    auto ex = new DBusException(&error, file, line, next);
+    dbus_error_free(&error);
+    throw ex;
+  }
+  return ret;
+}
+
+/++
+  Thrown when a DBus error code was returned by libdbus.
++/
+class DBusException : Exception {
+  private this(
+    scope DBusError *err,
+    string file = __FILE__,
+    size_t line = __LINE__,
+    Throwable next = null
+  ) pure nothrow {
+    import std.string : fromStringz;
+
+    super(err.message.fromStringz().idup, file, line, next);
+  }
+}
+

source/ddbus/thin.d

@@ -12,23 +12,8 @@ import std.conv;
 import std.range;
 import std.algorithm;
 
-class DBusException : Exception {
-  this(DBusError *err) {
-    super(err.message.fromStringz().idup);
-  }
-}
-
-T wrapErrors(T)(T delegate(DBusError *err) del) {
-  DBusError error;
-  dbus_error_init(&error);
-  T ret = del(&error);
-  if(dbus_error_is_set(&error)) {
-    auto ex = new DBusException(&error);
-    dbus_error_free(&error);
-    throw ex;
-  }
-  return ret;
-}
+// This import is public for backwards compatibility
+public import ddbus.exception : wrapErrors, DBusException;
 
 struct ObjectPath {
   private string _value;