add C.screen_width and C.screen_height methods

ext/svi/svi.c

@@ -1,5 +1,30 @@
 #include <ruby.h>
+#include <curses.h>
+
+static int Screen_Width = -1;
+static int Screen_Height = -1;
+
+VALUE Rb_screen_width(void)
+{
+    return INT2FIX(Screen_Width);
+}
+
+VALUE Rb_screen_height(void)
+{
+    return INT2FIX(Screen_Height);
+}
 
 void Init_svi(void)
 {
+    /* Determine screen dimensions. */
+    initscr();
+    getmaxyx(stdscr, Screen_Height, Screen_Width);
+    endwin();
+
+    VALUE svi_module = rb_define_module("Svi");
+    VALUE c_module = rb_define_module_under(svi_module, "C");
+    rb_define_module_function(c_module, "screen_width",
+            Rb_screen_width, 0);
+    rb_define_module_function(c_module, "screen_height",
+            Rb_screen_height, 0);
 }