trace_processor: Reland ABS_TIME_STR

Currently ABS_TIME_STR can be very slow so just landing trace_processor
side first. Also updated the CHANGELOG and bumped the API version.

Change-Id: Ib9a4056a395d39eb13aa017f2c77e23eeb0d932f

CHANGELOG

diff --git a/CHANGELOG b/CHANGELOG
index 99e6c4b..0f1ec0a 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,10 +1,11 @@
-Unreleased:
+CHANGELOGUnreleased:
   Tracing service and probes:
     * Android perf profiler ("linux.perf" data source) and Java heap snapshots
       ("android.java_hprof") now support a single wildcard (*) in the config
       options that name process command lines to target.
   Trace Processor:
-    *
+    * Added ABS_TIME_STR function which converts a trace timestamp to
+      an ISO8601 string.
   UI:
     *
   SDK: