Added logging, refactored versioning; STB is now included

- Added logging
- Rewrote versioning code
- Refactored dependency management
  - STB (stb_image.h) is now included
  - All other dependencies now use find_package
- Cross-compilation from Linux to Windows is now possible

main/logging.h

@@ -0,0 +1,64 @@
+#pragma once
+
+#include "boost/core/noncopyable.hpp"
+#include <ostream>
+
+namespace progressia {
+namespace main {
+
+namespace detail {
+
+class LogSink : private boost::noncopyable {
+  private:
+    bool isCurrentSink;
+
+    std::ostream &getStream() const;
+
+    template <typename T> void put(const T &x) const {
+        if (isCurrentSink) {
+            getStream() << x;
+        }
+    }
+
+  public:
+    LogSink(bool isCurrentSink);
+    ~LogSink();
+
+    LogSink(LogSink &&);
+
+    template <typename T>
+    friend const LogSink &operator<<(const LogSink &sink, const T &x) {
+        sink.put(x);
+        return sink;
+    }
+};
+} // namespace detail
+
+enum class LogLevel {
+    // Only interesting when investigating a problem.
+    DEBUG,
+    // A regular user may want to see this.
+    INFO,
+    // All users should read this; if message persists, something is wrong.
+    WARN,
+    // Something is definitely wrong, but we're not crashing (yet).
+    ERROR,
+    // This is why the game is about to crash.
+    FATAL
+};
+
+detail::LogSink log(LogLevel, const char *start = nullptr);
+
+namespace logging {
+detail::LogSink debug(const char *start = nullptr);
+detail::LogSink info(const char *start = nullptr);
+detail::LogSink warn(const char *start = nullptr);
+detail::LogSink error(const char *start = nullptr);
+detail::LogSink fatal(const char *start = nullptr);
+} // namespace logging
+
+void initializeLogging();
+void shutdownLogging();
+
+} // namespace main
+} // namespace progressia