Make 6.0.0 release
Make 6.0.0 release

Changed behavior (giving the major version bump):

  - cbf32e2 ("Expand environment variables in strings directly") makes
    'option env' "bounce" symbols redundant, though they are still
    supported for backwards compatibility (with the caveat that they
    must have the same name as the environment variables they
    reference to preserve behavior).

    A warning is printed if 'option env="FOO"' appears on a symbol
    that's not named FOO.

    This change will likely appear in the C tools soon as well.

Other new features:

  - The menuconfig implementation is now bundled in the PyPI package,
    along with implementations of the Kconfig oldconfig and
    all{def,no,yes,mod}config tools.

    A genconfig script is provided for generating a C header from the
    configuration, as well as (optionally) the sync_deps() directory
    structure for implementing incremental builds.

  - 63a4418 ("Record which MenuNode has each property") makes it
    possible to generate documentation for symbols defined in multiple
    locations with each property shown on the right definition. See
    genrest.py in Zephyr.

    This change also cleans up the parsing code a bit. Dependency
    propagation is now done after parsing, in _finalize_tree().

  - 94020be ("Make Kconfig._choices public") and fc73c46 ("Provide lists
    with all menus and comments") gives easier access to Kconfig items
    of a specific type, without having to walk the menu tree. This turns
    out to be handy e.g. when generating documentation and implementing
    search.

Improvements and new warnings:

  - da40c01 ("Force encoding to UTF-8 by default on Python 3")

  - 7427079 ("Get rid of the predefined UNAME_RELEASE symbol")

  - f64591c ("Warn if prompt contains leading or trailing whitespace")

  - c14e411 ("Warn if quotes are omitted around string defaults")

Misc. minor refactoring and cleanup has been done as well.

ulfalizer/Kconfiglib,ulfalizer/Kconfiglib