Dl-plus

**WARNING: this build is broken, use [0.4.0.post1](https://github.com/un-def/dl-plus/releases/tag/0.4.0.post1) instead.**

Features

* Backend management commands. It is now possible to install backends using `dl-plus` itself. Backends are installed into the `dl-plus` config directory, therefore, they are not visible to/do not interfere with other packages installed into the same Python environment.
- `dl-plus --cmd backend install [NAME [VERSION]]` installs the backend package into the `dl-plus` config directory.
- `dl-plus --cmd backend info` prints information about the configured backend.
* A new optional `[backend-options]` config section. The section has exactly the same format as the `youtube-dl` config (one can think of it as the `youtube-dl` config embedded into the `dl-plus` one). If this section is present, even if it is empty, it overrides `youtube-dl` own config(s) (`--ignore-config` is used internally).
* `youtube-dl`–compatible mode. When `dl-plus` is run as `youtube-dl` (e.g., via a symlink), it disables all additional command line options. The config file is still processed.

Improvements

* `-U`/`--update` is now handled by `dl-plus` itself rather than passing it to the underlying backend. For now, it says that this feature is not yet implemented (and it is not).

Features

Extractor API

* Two new attributes were added: `DLP_BASE_URL` and `DLP_REL_URL`. If set, they are used to compute the `_VALID_URL` value.
* A new `dlp_match` method was added. It returns a `re.Match` object for a given URL.

Improvements

* Remove duplicates when expanding the extractor list from the config (`[extractors.enable]`) or the command line arguments (`--extractor`). For example, `-E twitch:vod -E twitch` will no longer include the `twitch:vod` extractor twice.

Internal Changes

* `dl_plus.extractor.Extractor` and `dl_plus.extractor.ExtractorError` are now loaded lazily. It is now possible to import modules from the `dl_plus.extractor` package without first initializing `dl_plus.ytdl`.

Features

* Configurable `youtube-dl`–compatible backends. `youtube-dl` is not a hardcoded dependency anymore, `dl-plus` can now work with any _compatible_ package (that is, any _compatible_ fork), even if its import path is different). As a result, `dl-plus` no longer installs `youtube-dl` automatically. The backend can be configured using the `--backend` command line option or the `backend` option in the `[main]` section on the config file (see below). The value is an import path of the backend (e.g., `youtube_dl` for `youtube-dl`).
* Configuration file support. The config provides used-defined default values for the command line options (that is, the config options have lower predecence than the command line ones). The default config location is `$XDG_CONFIG_HOME/dl-plus/config.ini` (*nix) or `%APPDATA%\dl-plus\config.ini` (Windows).

Changes

* The generic extractor is no longer included in the `:builtins:` list. That is, one should use `-E :builtins: -E generic` to get **all** built-in extractors.
* Built-in extactors are now grouped by their names splitted by colons. For example, `-E twitch` is now expanded to a list of all `twitch:*` extractors (previously, one should specify each `twitch:*` extractor manually: `-E twitch:stream -E twitch:vod -E ...`).

Fixes

* `youtube-dl` config processing was restored. The config was simply ignored in the previous version.

Improvements

* The `--extractor` and `--force-generic-extractor` command-line options are mutually exclusive now.
* Added the `--dlp-version` command-line option to check `dl-plus` version (the `--version` option shows the version of the backend).

The first public release.