Update CHANGELOG after clean up on the operators table

by making it sane and clean in case we want to add
custom operators in the future.

The operator table with suggestions of extension points
(not yet implemented) can be found in the elixir_parser.yrl
file.

The only backwards incompatible change is the precedence
of the operators used by the Bitwise module.

Author: José Valim

CHANGELOG.md

@@ -27,6 +27,7 @@
   * [Typespec] Deprecate `(fun(...) -> ...)` in favor of `(... -> ...)`
 
 * backwards incompatible changes
+  * [Bitwise] Precedence of operators used by the Bitwise module were changed. Check `elixir_parser.yrl` for more information.
   * [File] `rm_rf` and `cp_r` now returns a tuple with three elements on failures
   * [Kernel] The quoted representation for `->` clauses changed from a tuple with two elements to a tuple with three elements to support metadata
   * [Mix] No longer support beam files on `mix local`