v0.1.3: Version 0.1.3

This release contains a change that sets 'seccomp=unconfined' with
Docker's '--security-opt' option when this program creates a new
container.  This option is necessary to install some packages, like
x11-libs/gdk-pixbuf, in a stage3 container with glibc >=2.34 on a GitHub
Actions runner.

v0.1.2: Version 0.1.2

This release contains only one substantial change: if this program does
not need to invoke the container engine's executable due to command-line
arguments like '--help' and '--version', it will no longer check for
existence of the executable.  This allows users to view this program's
help text and version information without a container engine installed,
which improves user experience.

Version 0.1.1

This release mainly focuses on internal improvements that should
marginally improve some operations' performance.  Some program output
messages have been updated to provide more information about what the
program has done or how it should be invoked.  Following setuptools's
deprecation of './setup.py install', the project's installation process
now relies on pip instead.

More detailed summary of changes:

- This program will no longer overwrite any MAKEOPTS definitions in
  /etc/portage/make.conf in the container to set the '-j' option.  It
  will now append a new line to the file that contains
  'MAKEOPTS="${MAKEOPTS} -jN"' to set it.

- Options for 'emerge' commands executed in the container will be set
  via the 'EMERGE_DEFAULT_OPTS' option in /etc/portage/make.conf instead
  of by including the options in every 'emerge' command initiated by
  this program.

- A comment line will be added above all new lines written by this
  program to /etc/portage/make.conf in the container, to indicate that
  those lines were added by this program.

- The container will be created and started via a single process
  invoking 'docker run -d' rather than two processes invoking
  'docker create' followed by 'docker start' respectively.

- When this program skips container clean-up before it exits, it will
  print a message to indicate the skip and include the container name in
  the message, making manual container clean-up more convenient.

- If the 'EBUILD_CMDER_DOCKER' environment variable is not set or is set
  to the default value, and the default container engine's executable is
  not available, a message about using this variable to specify an
  alternative container engine will be printed.

- The 'setup.py' script has been removed as a result of the
  './setup.py install' command's deprecation.  To install this program,
  please use 'pip install .' instead.  More information about
  installation and uninstallation of this program is available under the
  "Installation" section in file README.md.

Version 0.1.0

v0.1.0

Initial release