Add two reference files for field ionization calc

All references to the files where each ionization model is calculated
have been collected in two new files:
    - `fieldIonizationCalc.def`
    - `fieldIonizationCalc.hpp`
and forward declarations are made in the `.def` file.

src/picongpu/include/particles/ionization/byField/fieldIonizationCalc.def

@@ -0,0 +1,46 @@
+/**
+ * Copyright 2015 Marco Garten
+ *
+ * This file is part of PIConGPU.
+ *
+ * PIConGPU is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PIConGPU is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with PIConGPU.
+ * If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+/** forward declarations for ionization algorithms
+ *
+ * ionization model has a < Name >
+ * so the algorithm is called "Algorithm< Name >"
+ */
+
+namespace picongpu
+{
+
+namespace particles
+{
+
+namespace ionization
+{
+
+    struct AlgorithmNone;
+
+    struct AlgorithmBSI;
+
+} // namespace ionization
+
+} // namespace particles
+
+} // namespace picongpu

src/picongpu/include/particles/ionization/byField/fieldIonizationCalc.hpp

@@ -0,0 +1,24 @@
+/**
+ * Copyright 2015 Marco Garten
+ *
+ * This file is part of PIConGPU.
+ *
+ * PIConGPU is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PIConGPU is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with PIConGPU.
+ * If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "particles/ionization/byField/BSI/AlgorithmBSI.hpp"
+#include "particles/ionization/None/AlgorithmNone.hpp"