Update CHANGELOG.md and docs for loop and pp.

CHANGELOG.md

@@ -14,6 +14,7 @@ All notable changes to this project will be documented in this file.
 - Correct arity for `marshal`
 - Add `flush` and `eflush`
 - Add `prompt` and `return` on top of signal for user friendly delimited continuations.
+- Fix possible segfault with malformed pegs.
 
 ## 1.7.0 - 2020-02-01
 - Remove `file/fileno` and `file/fdopen`.

src/boot/boot.janet

@@ -481,7 +481,8 @@
   \t:iterate - repeatedly evaluate and bind to the expression while it is truthy.\n
   \t:range - loop over a range. The object should be two element tuple with a start
   and end value, and an optional positive step. The range is half open, [start, end).\n
-  \t:down - Same as range, but loops in reverse.\n
+  \t:down - Same as range, but breaks the loop when the binding is less than or equal to end.
+  Step should still be a positive integer.\n
   \t:keys - Iterate over the keys in a data structure.\n
   \t:pairs - Iterate over the keys value pairs in a data structure.\n
   \t:in - Iterate over the values in an indexed data structure or byte sequence.\n
@@ -1280,7 +1281,7 @@
   nil)
 
 (defn pp
-  "Pretty print to stdout or (dyn :out)."
+  `Pretty print to stdout or (dyn :out). The format string used is (dyn :pretty-format "%q").`
   [x]
   (printf (dyn :pretty-format "%q") x)
   (flush))