Add Braille canvas and basic line plots

demo.ss

@@ -0,0 +1,13 @@
+#!/usr/bin/env gxi
+
+(export main)
+
+(import :std/misc/string
+	:dlozeve/fancy/format
+	:dlozeve/uniplot/lineplot)
+
+(def (main . args)
+  (let* ((xs (iota 1000 0 0.01))
+	 (ys1 (map cos xs))
+	 (ys2 (map sin xs)))
+    (displayln (line-plot [xs ys1 ys2]))))