Add logging controls to the API

Control verbosity and choose a file to output to.

include/loot/api.h

@@ -37,9 +37,33 @@
 #include "loot/exception/game_detection_error.h"
 #include "loot/exception/git_state_error.h"
 #include "loot/enum/game_type.h"
+#include "loot/enum/log_verbosity.h"
 #include "loot/loot_version.h"
 
 namespace loot {
+/**@}*/
+/**********************************************************************//**
+ *  @name Logging Functions
+ *************************************************************************/
+/**@{*/
+
+/**
+ * @brief Set the API's logging verbosity.
+ * @details The default is ``LogVerbosity::off``.
+ * @param verbosity
+ *        The logging verbosity to set.
+ */
+LOOT_API void SetLoggingVerbosity(LogVerbosity verbosity);
+
+/**
+ * @brief Set the file path that logging statements are written to.
+ * @details If no file is set the default behaviour is to print logging
+ *          statements to the console.
+ * @param path
+ *        The log file path.
+ */
+LOOT_API void SetLogFile(const std::string& path);
+
 /**@}*/
 /**********************************************************************//**
  *  @name Version Functions

include/loot/enum/log_verbosity.h

@@ -0,0 +1,48 @@
+/*  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_LOG_VERBOSITY
+#define LOOT_LOG_VERBOSITY
+
+/**
+ * The namespace used by the LOOT API.
+ */
+namespace loot {
+/**
+ * @brief Codes used to specify the preferred language for messages when
+ *        evaluating masterlists and userlists.
+ * @details If a message is not available in the preferred language, its English
+ *          string will be used. Note that messages with only one language
+ *          string are assumed to be written in English, but this cannot be
+ *          guaranteed (any violations should be reported as bugs so that they
+ *          can be fixed).
+ */
+enum struct LogVerbosity : unsigned int {
+  off,
+  warning,
+  trace,
+};
+}
+
+#endif