Add deprecation plans to changelog (see #440) [ci skip]

Author: yaauie

CHANGELOG.md

@@ -1,3 +1,17 @@
+# 4.x (unreleased)
+
+## Planned breaking changes:
+* `Redis#client` will no longer expose the underlying `Redis::Client`;
+  it has not yet been determined how 4.0 will expose the underlying
+  functionality, but we will make every attempt to provide a final minor
+  release of 3.x that provides the new interfaces in order to facilitate
+  a smooth transition.
+
+* Ruby 1.8.7 (and the 1.8 modes of JRuby and Rubinius) will no longer be
+  supported; 1.8.x entered end-of-life in June of 2012 and stopped receiving
+  security updates in June of 2013; continuing to support it would prevent
+  the use of newer features of Ruby.
+
 # 3.1.x (unreleased)
 
 * Added debug log sanitization (#428).