Split backend helpers.h up

windows_encoding_converters.h contains the ToWinWide/FromWinWide
functions shared by the API and GUI, and crc.h contains GetCrc32().

include/loot/windows_encoding_converters.h

@@ -0,0 +1,60 @@
+/*  LOOT
+
+    A load order optimisation tool for Oblivion, Skyrim, Fallout 3 and
+    Fallout: New Vegas.
+
+    Copyright (C) 2012-2016    WrinklyNinja
+
+    This file is part of LOOT.
+
+    LOOT 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.
+
+    LOOT 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 LOOT.  If not, see
+    <https://www.gnu.org/licenses/>.
+    */
+
+#ifndef LOOT_BACKEND_HELPERS_HELPERS
+#define LOOT_BACKEND_HELPERS_HELPERS
+
+#ifdef _WIN32
+
+#include <string>
+
+#   ifndef UNICODE
+#       define UNICODE
+#   endif
+#   ifndef _UNICODE
+#      define _UNICODE
+#   endif
+#   include "windows.h"
+#   include "shlobj.h"
+#   include "shlwapi.h"
+
+namespace loot {
+inline std::wstring ToWinWide(const std::string& str) {
+  size_t len = MultiByteToWideChar(CP_UTF8, 0, str.c_str(), str.length(), 0, 0);
+  std::wstring wstr(len, 0);
+  MultiByteToWideChar(CP_UTF8, 0, str.c_str(), str.length(), &wstr[0], len);
+  return wstr;
+}
+
+inline std::string FromWinWide(const std::wstring& wstr) {
+  size_t len = WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), wstr.length(), NULL, 0, NULL, NULL);
+  std::string str(len, 0);
+  WideCharToMultiByte(CP_UTF8, 0, wstr.c_str(), wstr.length(), &str[0], len, NULL, NULL);
+  return str;
+}
+}
+
+#endif
+
+#endif