Update change log.

CHANGELOG.md

@@ -8,11 +8,26 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- The new handler osmium::handler::CheckOrder can be used to check that a
+  file is properly ordered.
+- Add new method to build OSM nodes, ways, relations, changesets, and areas
+  in buffers that wraps the older Builder classes. The new code is much easier
+  to use and very flexible. There is no documentation yet, but the tests in
+  `test/t/builder/test_attr.cpp` can give you an idea how it works.
+- Add util class to get memory usage of current process on Linux.
+
 ### Changed
 
+- New Buffer memory management speeds up Buffer use, because it doesn't clear
+  the memory unnecessarily.
+
 ### Fixed
 
 - osmium::Box::extend() function now ignores invalid locations.
+- Install of external library headers.
+- Check way has at least one node before calling `is_closed()` in area
+  assembler.
+- Declaration/definition of some friend functions was in the wrong namespace.
 
 
 ## [2.5.4] - 2015-12-03