1.0.0 -- semantic versioning from here

This release represents a milestone in the development of the extension.
The package is reorganized to be a collection of more self-contained
mini-packages, each with its own set of tests.

Developer documentation and guidelines have been added to aid further
development. One particular goal is to establish datalad-next as a proxy
for importing datalad-core functionality for other extensions. Direct imports
from datalad-core can be minimized in favor of imports from datalad-next.
This helps identifying functionality needed outside the core package,
and guides efforts for future improvements.

The 1.0 release marks the switch to a more standard approach to semantic
versioning. However, although a substantial improvements have been made,
the 1.0 version nohow indicates a slowdown of development or a change in the
likelihood of (breaking) changes. They will merely become more easily
discoverable from the version label alone.

Notable high-level features introduced by this major release are:

• The new UrlOperations framework to provide a set of basic operations like
  download, upload, stat for different protocols. This framework can be
  thought of as a replacement for the "downloaders" functionality in
  datalad-core -- although the feature list is not 100% overlapping. This new
  framework is more easily extensible by 3rd-party code.

• The Constraints framework elevates parameter/input validation to the next
  level. In contrast to datalad-core, declarative input validation is no longer
  limited to the CLI. Instead, command parameters can now be validated regardless
  of the entrypoint through which a command is used. They can be validated
  individually, but also sets of parameters can be validated jointly to implement
  particular interaction checks. All parameter validations can now be performed
  exhaustive, to present a user with a complete list of validation errors, rather
  then the fail-on-first-error method implemented exclusively in datalad-core.
  Validation errors are now reported using dedicated structured data type to aid
  their communication via non-console interfaces.

• The Credentials system has been further refined with more homogenized
  workflows and deeper integration into other subsystems. This release merely
  represents a snapshot of continued development towards a standardization of
  credential handling workflows.

• The annex remotes uncurl and archivist are replacements for the
  datalad-core implementations datalad and datalad-archive. The offer
  substantially improved configurability and leaner operation -- built on the
  UrlOperations framework.

• A growing collection of iterator (see iter_collections) aims to provide
  fast (and more Pythonic) operations on common data structures (Git worktrees,
  directories, archives). The can be used as an alternative to the traditional
  Repo classes (GitRepo, AnnexRepo) from datalad-core.

• Analog to UrlOperations the ArchiveOperations framework aims to provide
  an abstraction for operations on different archive types (e.g., TAR). The
  represent an alternative to the traditional implementations of
  ExtractedArchive and ArchivesCache from datalad-core, and aim at leaner
  resource footprints.

• The collection of runtime patches for datalad-core has been further expanded.
  All patches are now individually documented, and applied using a set of standard
  helpers (see http://docs.datalad.org/projects/next/en/latest/patches.html).

For details, please see the changelogs of the 1.0.0 beta releases below.

💫 Enhancements and new features

• TarArchiveOperations is the first implementation of the ArchiveOperations
  abstraction, providing archive handlers with a set of standard operations:
  • open to get a file object for a particular archive member
  • __contains__ to check for the presence of a particular archive member
  • __iter__ to get an iterator for processing all archive members
    #415 (by @mih)

🐛 Bug Fixes

• Make TarfileItem.name be of type PurePosixPath to reflect the fact
  that a TAR archive can contain members with names that cannot be represent
  unmodified on a non-POSIX file system.
  #422 (by @mih)
  An analog change is done for ZipfileItem.name.
  #409 (by @christian-monch)

• Fix git ls-file parsing in iter_gitworktree() to be compatible with
  file names that start with a tab character.
  #421 (by @christian-monch)

📝 Documentation

• Expanded guidelines on test implementations.

• Add missing and fix wrong docstrings for HTTP/WebDAV server related fixtures.
  #445 (by @adswa)

🏠 Internal

• Deduplicate configuration handling code in annex remotes.
  #440 (by @adswa)

🛡 Tests

• New test fixtures have been introduced to replace traditional test helpers
  from datalad-core:

  • datalad_interactive_ui and datalad_noninteractive_ui for testing
    user interactions. They replace with_testsui.
    #427 (by @mih)

• Expand test coverage for create_sibling_webdav to include recursive
  operation.
  #434 (by @adswa)