add mebos, a multiplexed ebos variant

`mebos` works similarly as `flow`, but in contrast to `flow`, `mebos`
only creates the deck in the common code path whilst the
'EclipseState' and the other higher-level parser objects are always
created internally by the vanguard. this approach avoids code
duplication and the worst effects of parser API creep.

to avoid having to compile non-trivial compile units multiple times,
the actual code of the variants is moved into `ebos_$VARIANT.{hh,cc}`
files and the respective compile units are each put into a small
static library whilst the main function of said libraries are invoked
by either the multiplexed or the respective specialized simulator's
`main()`. This is also somewhat similar of how `flow` works, with the
difference that `mebos` uses the blackoil variant to determine the
parameters it needs to know for parsing the deck instead of
introducing a "fake" type tag for this. The rationale is to reduce
compile time compared to the "fake type tag" approach and -- to a
lesser extend -- avoid unnecessary copy-and-pasting of code. In
particular, this means that for the vast majority of cases, only one
place needs changed in the code for all `ebos` variants if, for
example, the parser API requires further objects in the future.

ebos/ebos_gasoil.hh

@@ -0,0 +1,44 @@
+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+/*
+  This file is part of the Open Porous Media project (OPM).
+
+  OPM 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 2 of the License, or
+  (at your option) any later version.
+
+  OPM 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 OPM.  If not, see <http://www.gnu.org/licenses/>.
+
+  Consult the COPYING file in the top-level source directory of this
+  module for the precise wording of the license and the list of
+  copyright holders.
+*/
+/*!
+ * \file
+ *
+ * \brief The function prototypes required to start the gas-oil variant of ebos
+ */
+#ifndef EBOS_GAS_OIL_HH
+#define EBOS_GAS_OIL_HH
+
+#include <opm/parser/eclipse/Deck/Deck.hpp>
+#include <opm/parser/eclipse/Parser/ParseContext.hpp>
+#include <opm/parser/eclipse/Parser/ErrorGuard.hpp>
+
+namespace Ewoms {
+void ebosGasOilSetDeck(Opm::Deck* deck,
+                         Opm::ParseContext* parseContext,
+                         Opm::ErrorGuard* errorGuard,
+                         double externalSetupTime);
+
+int ebosGasOilMain(int argc, char** argv);
+}
+
+#endif