The new dedicated docs directory has been introduced after a discussion
on GitHub[1].

Main issue it is addressing is the reduction of too many README files in
the project root directory. The new directory is dedicated for notes and
quick documentation files that either can't be put in the manual or wiki
pages or that relate to the php-src repository specifically and need to
live together with the source code.

Also the `docs` directory is by GitHub used for some repository
configuration files such as pull request templates, and contributing
documentation helper files that are integrated in the interface.

[1]: https://github.com/php/php-src/pull/3988

This patch joins two very much related pieces of docs together in a
single file dedicated to all sorts of contributing info.

Some more changes:
- Branches info copied from the current master branch
- LXR and bonsai info removed
- Duplicated info reduced a bit
- Security branch updated to 7.1
- Refactor intro for Git commit rules
- Updated README.GIT-RULES file usage in win32/build/confutils.js
- Refactored configure.ac

The more proper place for shell scripts dedicated for development, and
releasing PHP should be the scripts/dev directory. Having a cleaner root
project directory helps find the main README.md and files relevant to
install PHP.

These scripts are also used by the release managers mostly who create
release packages and aren't used often by the majority of developers
working on and installing PHP.

According to current practice, and as discussed with other RMs.

While the major version is different, and the minor version may be
different, the revision and the extra should always be synced, as
recently discussed on the release manager's list.  We add the
respective info to README.RELEASE_PROCESS, to not forget about it in
the future.

Cf. <http://svn.php.net/viewvc?view=revision&revision=346164>.

As of PHP 5.3, there are no more Windows specific version keys.

According to a respective RFC[1], the MD5 checksums have been removed
from the release notes and the API.  Also, no checksums are generated
after uploading the tarballs to the user directories
on downloads.php.net.

[1] <https://wiki.php.net/rfc/release-md5-deprecation>