Document a couple of words in random

Add a word to get a random 256-bit integer

extra/random/random-docs.factor

@@ -21,3 +21,11 @@ HELP: random
 { $values { "seq" "a sequence" } { "elt" "a random element" } }
 { $description "Outputs a random element of the sequence. If the sequence is empty, always outputs " { $link f } "." }
 { $notes "Since integers are sequences, passing an integer " { $snippet "n" } " yields a random integer in the interval " { $snippet "[0,n)" } "." } ;
+
+HELP: big-random
+{ $values { "n" "an integer" } { "r" "a random integer" } }
+{ $description "Outputs an integer with n bytes worth of bits." } ;
+
+HELP: random-256
+{ $values { "r" "a random integer" } }
+{ $description "Outputs an random integer 256 bits in length." } ;

extra/random/random.factor

@@ -93,6 +93,8 @@ PRIVATE>
 : big-random ( n -- r )
     [ drop (random) ] map >c-uint-array byte-array>bignum ;
 
+: random-256 ( -- r ) 8 big-random ; inline
+
 : random ( seq -- elt )
     dup empty? [
         drop f