added scrollback patch and modified it to only scroll half a page

patches/scrollback_ringbuffer/st_h.diff

@@ -0,0 +1,12 @@
+diff --git a/st.h b/st.h
+index fd3b0d8..3cea73b 100644
+--- a/st.h
++++ b/st.h
+@@ -19,6 +19,7 @@
+ 
+ #define TRUECOLOR(r,g,b)	(1 << 24 | (r) << 16 | (g) << 8 | (b))
+ #define IS_TRUECOL(x)		(1 << 24 & (x))
++#define HISTSIZE            2000
+ 
+ enum glyph_attribute {
+ 	ATTR_NULL       = 0,