Added contributor and updated README to add AIX.

CONTRIBUTORS.txt

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 717ffc1..4a804a0 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -91,3 +91,6 @@
   William Orr <will@worrbase.com>
     * Fixed detection of sched_yield on Solaris.
     * Added atomicops for Solaris
+  Andrew Paprocki <andrew@ishiboo.com>
+    * Fixed minor IBM xlC compiler build issues
+    * Added atomicops for AIX (POWER)