Release Notes; upgrade information mainly.
Features/major bugfixes are listed in NEWS

portage-2.2
==================================

* The python namespace for portage has been sanitized, all portage related code
  is now contained within the portage namespace. External script should be updated
  accordingly, though links exist for backward compability.
* The "save_summary" and "echo" elog modules are now enabled by default. Setting
  PORTAGE_ELOG_SYSTEM in make.conf will override this, so if you don't want elog
  set PORTAGE_ELOG_SYSTEM="" in make.conf
* -* support in package.keywords was changed as it was inconsistent with 
  ACCEPT_KEYWORDS behavior (also see http://dev.gentoo.org/~genone/docs/KEYWORDS.stupid).
  Previously having -* in package.keywords matched packages with KEYWORDS="-*", 
  now it resets the ACCEPT_KEYWORDS list for the given atom like it does when
  used in ACCEPT_KEYWORDS.
  For packages that don't specify any other KEYWORDS you can use the new ** token
  as documented in portage(5) to disable KEYWORDS filtering completely.

portage-2.1.3
==================================

* The unmerge process will remove any file that is not claimed by another
  package in the same slot and is not protected by CONFIG_PROTECT, even if the
  modification time or checksum differs from the file that was originally
  installed.  The old behavior is still available by adding -unmerge-orphans
  to FEATURES.

portage-2.1.2
==================================

* Depending on the number of packages installed, users may notice a difference
  in the time taken for dependency calculations.  This performance penalty is
  due to the addition of important new features which include the ability to
  detect reverse blockers, the building of a complete dependency graph, and the
  ability to use installed packages to satisify dependencies even after their
  ebuilds have been removed from the portage tree.
* emerge does not necessarily update build time dependencies that are not
  strictly required.  See the --with-bdeps option in the emerge(1) man page.

portage-2.1.1
==================================

* emerge --search doesn't use regular expressions now anymore by default, so
  emerge --search dvd+rw-tools now works as expected. Regular expressions can be enabled
  by prefixing the search string with %. 
* emerge --depclean algorithm is much safer than the old one.
* emerge --newuse detects changes in IUSE that previously went undetected.

portage-2.1
==================================

* new cache framework, breaking all old cache modules.
  If you're having problems with portage_db_cdb, this is likely the cause.
* USE flag output ordering has changed.  The old ordering is now an option
  by the name of --alphabetical.  Adding the option to EMERGE_DEFAULT_OPTS
  in make.conf will restore the old behaviour permanently.
* The deprecated --inject has been removed, use /etc/portage/profile/package.provided
* The deprecated --upgradeonly has been removed, use /etc/portage/package.* 
  instead.
* 'emerge sync' has been deprecated, use 'emerge --sync' instead (same 
  for other actions)
* Tools that call emerge should override the EMERGE_DEFAULT_OPTS environment
  variable or use the emerge --ignore-default-opts option.
* rsync option handling has been redesigned, instead of RSYNC_* variables
  use PORTAGE_RSYNC_EXTRA_OPTS from now on.
* autouse (use.defaults) has been deprecated by specifying USE_ORDER in make.defaults
  Users may still turn this back on by specifying USE_ORDER="env:pkg:conf:auto:defaults"
  in make.conf.  Interested in figuring out what use flags were turned off?  Check out
  /usr/portage/profiles/base/use.defaults and other use.defaults files that correspond 
  to your profile.