add unicode control-picturizer and docs

extra/unicode/control-pictures/authors.txt

@@ -0,0 +1 @@
+Pi

extra/unicode/control-pictures/control-pictures-docs.factor

@@ -0,0 +1,16 @@
+! Copyright (C) 2017 Pi.
+! See http://factorcode.org/license.txt for BSD license.
+USING: help.markup help.syntax help.topics strings ;
+IN: unicode.control-pictures
+
+HELP: control-pictures
+{ $values
+    { "string" string }
+}
+{ $description "Transforms C0 control characters into their corresponding Control Picture block codepoints." } ;
+
+ARTICLE: "unicode.control-pictures" "Control Pictures"
+"The " { $vocab-link "unicode.control-pictures" } " vocabulary provides a utility word " { $link control-pictures } " for transforming characters in the nonprintable ASCII C0 block to their representations in the Control Pictures block. It has no effect on any other characters."
+;
+
+ABOUT: "unicode.control-pictures"

extra/unicode/control-pictures/control-pictures.factor

@@ -0,0 +1,18 @@
+! Copyright (C) 2017 Pi.
+! See http://factorcode.org/license.txt for BSD license.
+USING: combinators kernel math sequences ;
+IN: unicode.control-pictures
+
+<PRIVATE
+
+: char>control-picture ( char -- char' )
+    {
+        { [ dup 0x20 < ] [ 0x2400 bitor ] }
+        { [ dup 0x7f = ] [ drop 0x2421 ] }
+        [ ]
+    } cond ;
+
+PRIVATE>
+
+: control-pictures ( string -- string )
+    [ char>control-picture ] map ;