Major refactoring but now centering text and sprites works. See Issue #16 for why only those and not anything else yet.

src/guecs/lel.cpp

@@ -50,6 +50,7 @@ namespace lel {
     int cell_height = grid_h / rows;
 
     for(auto& row : grid) {
+      // BUG: see issue #16
       size_t columns = row.size();
       int cell_width = grid_w / columns;
       assert(cell_width > 0 && "invalid cell width calc");