Updated CHANGELOG for 0.20.1-rc3.
Replace os::Release with Version.

Review: https://reviews.apache.org/r/25755
Updated callers to os::release in mesos.

Review: https://reviews.apache.org/r/25780
Fixed a signed comparision issue in Version.
Fixed example frameworks to launch tasks based on offered resources.

Review: https://reviews.apache.org/r/25801
Fixed example frameworks to fail fast on an unexpected status udpate.

Review: https://reviews.apache.org/r/25805
Hold on to unacknowledged terminal tasks in the Master.

Review: https://reviews.apache.org/r/25567
Added tests for terminal unacknowledged tasks in the Master.

Review: https://reviews.apache.org/r/25568
Fixed a segfault regression in the master.

Review: https://reviews.apache.org/r/25810
Updated a comment regarding GCC 4.7 in configure.ac and some syntax
formatting.

Review: https://reviews.apache.org/r/25218
Ignore terminal task resources in the Master's Framework struct.

Review: https://reviews.apache.org/r/25844
Fixed an executor accounting bug in framework re-registration.

Review: https://reviews.apache.org/r/25843
Fixed an issue with colored output in post-reviews.py.

Review: https://reviews.apache.org/r/25819
Refactored Node class in libprocess.

Moved class Node out of process.cpp and into its own header as a part
of refactoring process.cpp.

Review: https://reviews.apache.org/r/25847
Allowed co-mounted cgroup subsystems to enable Mesos on machines with
systemd.

Review: https://reviews.apache.org/r/25858
Refactored the environment-based test filtering.

Review: https://reviews.apache.org/r/25569
Removed duplicate error messaging in Docker::create.
Added support for getting socket diagnosis information.

Review: https://reviews.apache.org/r/25948
Added variadic strings join.

There is a second version of the variadic join which takes a reference
to a stringstream as a parameter. This is handy when strings::join is
just a part of a larger string manipulation.

Review: https://reviews.apache.org/r/25789
Refactored libprocess Help to reduce compile time.

Reduces compile time overall by ~1/3rd. Move implementation of
libprocess help into cpp file.  Use strings::join to refactor macro
expansion that was injecting lots of overhead even when the expanded
functions were not used.

Review: https://reviews.apache.org/r/25798