* Inform about providers in `alr get`

* Test for the change

* Remainders of the config --> settings refactor

* Fix Windows-only builtins

* Refactor `ALR_CONFIG` to `ALIRE_SETTINGS`

* Replace --config with --settings

* Code review

* Post-merge fix

* config.toml --> settings.toml

* Prepend comment in `config.toml` about migration

* Remove file touching

* Refactor `ALR_CONFIG` to `ALIRE_SETTINGS`

* Code review

To avoid mixing top levels, also nest the cache too.

* Refactor `Alire.Config.*` as `Alire.Settings.*`

* Refactor Windows-only files

* Missing dependencies in testsuite documentation.

Required package 'pexpect' is not installed as a dependency of
'e3-testsuite', so is has to be explicitly installed.

Neither 'e3-testsuite' nor 'e3-core' depend on it:

$ pip show e3-testsuite e3-core
Name: e3-testsuite
Version: 26.0
Summary: E3 testsuite
Home-page:
Author: AdaCore
Author-email: info@adacore.com
License: GPLv3
Location: /home/ada/opt/alire/venv/lib/python3.10/site-packages
Requires: e3-core
Required-by:
---
Name: e3-core
Version: 22.4.0
Summary: E3 core. Tools and library for building and testing software
Home-page: https://github.com/AdaCore/e3-core
Author: AdaCore
Author-email: info@adacore.com
License: GPLv3
Location: /home/ada/opt/alire/venv/lib/python3.10/site-packages
Requires: colorama, ld, packaging, psutil, python-dateutil, pyyaml, requests, requests-cache, requests-toolbelt, setuptools, stevedore, tqdm
Required-by: e3-testsuite

* Install pip dependencies using requirements.txt

Both 'alr -c' and 'alr --config' throw exceptions because a required
parameter is missing.

This fix handle missing parameter of config switch in the same way as, for
example, 'alr -C' and 'alr --chdir': an error message informs the user that a
required parameter is missing.

Since it affects the place where the argument can be used, the user
has to be aware of that.

This change is introduced to tackle the confusion between the
configuration of the Alire commands and operations, and the
configuration of crates.

`alr config` is still available and should work as before with the
exception of a deprecation warning message.

* Remove --[un]install, --install-dir

* Patch tests

* User changes

* review of --install et al. removal

* Fix test broken by new crate hash

* Package to track future features

* Loading metadata and explicit binary

* bug box in case of Program_Error

* Fix optionally appearing address in error location

* alire-errors.ads: typo

* Don't run OS initialization during elaboration

As this makes impossible to tweak such initialization with `alr config`.

* Make msys live inside overriden config path by default

* Better explanation in alr.py

* Fix config loading before Windows builtins

* Reinstate lost style checks

* Explicit style checks and corresponding fixes

* Update the supported values of the os and distribution parameters.

* Use new `distribution-unknown`

---------

Co-authored-by: John Serock <1468970+serock@users.noreply.github.com>

...its variable name which is `distribution`

As this makes impossible to tweak such initialization with `alr config`.

* Intepret environment values as paths

This is the likely intended behavior. Down the road we can have a way to have
literal values in these strings.

* Fixes for Windows brokenness

...on outdated port definitions

When a complete solution is printed (`alr show|with --solve`), the "external"
section is now named "missing" (which is what it actually meant).

When a diff is show that contains missing dependencies, a new section is
appended containing separately all missing dependencies, labeled as such:
```
$ alr -f with hello unobtanium
Requested changes:

   ✓ hello      ^1.0.2 (add)
   ✓ unobtanium *      (add)

Changes to dependency solution:

   New solution is incomplete.
   +        hello      1.0.2 (new)
   Missing:
   +❗      unobtanium *     (new,missing:unknown)
```

* Basis for `build --stop-after`

* Implement build stages

* Test for new feature

* User changes

* Remove `sudo` that isn't available on Windows

* Code review

* s/Build_Stages/Stop_Points/