Convention is that after `--` no more switches are to be parsed.

* Procedures to ensure the stored value has the wanted type

* Add Get_As_String variant with default

* Fix null pointer

* Code review

* Leave just the variant with Default with "" as default

* Encode wwstrings as utf8

* Further fixes related to UTF-8

* Regen config for use as pin

* Fix new warning from GNAT 12

* Bump version as this is breaking without -gnatW8

* Remove redundant switch

* Code review

Test latest toolchain versions and use cache-enabled `alr` action.

Also store a default config with release configuration, for direct use of the
library without Alire.

* Give hint when invalid subcommand switch is valid global

* Improve wording

This may avoid an infinite loop reported on macOS

For compatibility with older GNAT versions.

The filtering mixed regex (default Filter pattern) and globing (actually system user in List).
Everything is now based on regex and documented.

With this change, the global command and subcommand can use the same
switches and they won't clash.

One of the goal here is to realize the full potential of the
Switches_As_Args option where parsing of sub-command switches is
disabled.

For example this will allow:
$ alr build -f -XTEST=plop # -f is passed to gprbuild and not to alr
$ alr exec bash -c "echo lol" # -c is passed to bash and not to alr

This will break some command line that used to work, for instance:
$ alr with hello --non-interactive

With this version multiple instances of configuration can exist in the
program.