Update TODO

TODO.md

@@ -15,7 +15,19 @@
 * Performance
     * cpu-target=native good?
     * mialloc good?
-* Track bytes transferred?
+    * use DashMap readable view when accessing torrent stats and possibly
+      also after modification of announcing peer and during collection
+      of response peers
+* Statistics
+    * Print stats for number of peers per torrent (median, 95th, 99th
+      percentile.) Use histogram crate?
+* bittorrent_udp
+    * ParseError enum maybe, with `Option<TransactionId>`
+    * Avoid allocating in conversion to bytes, send in a mutable buffer
+      instead, which is reused over requests
+    * Avoid heap allocation in general if it can be avoided?
+    * quickcheck tests for conversions
+    * other unit tests?
 
 ## Don't do