system: try to autodetect the data directory from the executable path;

currently works for images (SDL and GDI+ loaders) and sound samples.

neercs/neercs.cpp

@@ -1,7 +1,7 @@
 //
 // Neercs
 //
-// Copyright: (c) 2012 Sam Hocevar <sam@hocevar.net>
+// Copyright: (c) 2012-2013 Sam Hocevar <sam@hocevar.net>
 //
 
 #if defined HAVE_CONFIG_H
@@ -70,6 +70,8 @@ Neercs::~Neercs()
 
 int main(int argc, char **argv)
 {
+    System::Init(argc, argv);
+
     Application app("Neercs", ivec2(800, 600), 60.0f);
 
 #if defined _MSC_VER && !defined _XBOX