Add CPython 3.12.0a3

Export detected shell environment in pyenv-init

There was a space at the beginning of the `git clone` command

In some advanced shell setups, the order of custom-added PATH entries is important.
We disregard it by default, always pushing shims to the front of PATH,
to ensure that Pyenv works even in poorly maintained shell environments
and with minimal hassle for non-export users
(an attempt to do the opposite (#1898) has ended in a disaster).
Some advanced users are however ready and able to carefully maintain their environment
and deal with breakages and inconvenience. This option is for them.

Likely in Ubuntu where it's only available as a snap

Fix compilation error when building OpenSSL 1.1.1q in MacOS 11+ for 3.9.15 and 3.8.15

Signed-off-by: Alex <aleksandrosansan@gmail.com>

* Document listing available versions in the tutorial (#1677)
* Reflect 3.7.15's extended support
* Document using development head with Homebrew
* Structurize the Upgrading section
* Fix Pyenv-latest documentation

It was moved to `pyenv-install`

CPython 3.11+ dropped support for --with-tcl-tk-*
in favor of pure pkgconfig

Fix compilation error when building OpenSSL 1.1.1q in MacOS 11+

"error: implicitly declaring library function 'memcmp'"
Downstream backport of https://github.com/openssl/openssl/issues/18720

For some reason checksum for `Python-3.11.0.tgz` file introduced in
0726e02e3a is invalid. Update that
checksum to ensure `pyenv install 3.11.0` works well on systems without
tar.xz support.

Co-authored-by: Ivan Pozdeev <vano@mail.mipt.ru>

Build CPython 3.12+ with --with-dsymutil in MacOS

Since 3.12, CPython can provide debug symbols in
Apple's nonstandard way, "dSYM bundles"

It has been unused since Travis dropped free plans

Add ability to easily skip all use of Homebrew