Improve highlighting structure

- switched to a sparse delta based map
- true lazy-loading to avoid any unneccessary allocations
- fixed windows management api

include/io/sysio.h

@@ -96,14 +96,19 @@ inline bool is_empty_cell(const ScreenCell &c) {
   return c.utf8.empty() || c.utf8 == " " || c.utf8 == "\x1b";
 }
 
+namespace io {
 extern std::vector<ScreenCell> new_screen;
+extern uint32_t rows, cols;
+extern bool show_cursor;
+extern std::vector<ScreenCell> old_screen;
+extern termios orig_termios;
+} // namespace io
 
 Coord start_screen();
 void end_screen();
 void set_cursor(uint8_t row, uint8_t col, uint32_t type,
                 bool show_cursor_param);
 void io_render();
-Coord get_size();
 
 KeyEvent read_key();