About "mentioned" badge and format improvements

Remove dead link for matreshka

This was not made coherent in merge 2420c16

Work around the last problems reported by the linter

This works around these problems:

README.md:191:3:   https://matrix.to/#/#ada-lang_Lobby:gitter.im  remark-lint:double-link
README.md:199:112: https://matrix.to/#/#ada-lang:matrix.org       remark-lint:double-link

Which are due to an issue in the linter: https://github.com/Scrum/remark-lint-double-link/pull/10

Closes #107

Merge pull request #108 from ohenley/add-license-1

Add CC0 license file using template

Merge pull request #111 from ohenley/awesome-lint-links

Fix issues reported by awesome-lint (double-link, awesome-list-item)

Merge branch 'master' into awesome-lint-links

Merge branch 'master' into add-license-1

Fix typo and restore original wording

Fix issues reported by awesome-lint (double-link, awesome-list-item)

Fixes these occurrences:
```
  ✖  266:122  https://github.com/AdaCore/ada_language_server               remark-lint:double-link
  ✖  289:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  302:69   List item description must start with valid casing           remark-lint:awesome-list-item
  ✖  322:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  343:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  346:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  350:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  384:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  402:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  449:3    https://github.com/AdaCore/ada_language_server               remark-lint:double-link
  ✖  492:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  523:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  537:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  562:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  573:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  574:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  590:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  695:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  724:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  725:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  735:3    Invalid list item link                                       remark-lint:awesome-list-item
  ✖  736:3    Invalid list item link                                       remark-lint:awesome-list-item
```

See issue #107

Remove license reference in README.md

Add CC0 license file using template

As recommended by:
https://github.com/sindresorhus/awesome/blob/main/pull_request_template.md#requirements-for-your-awesome-list

This will allow removing these awesome-lint errors:
```
README.md:1:1:   License was not detected by GitHub                           remark-lint:awesome-github
README.md:1:1:   Forbidden license section found                              remark-lint:awesome-license
```

Update to HTTPS all the links working with that protocol

Merge pull request #112 from mgrojo/lychee-link-checker

New better link checker and dead links fixed

Remove deprecated a2js. Added adawebui.

Recommended by author. See https://github.com/godunko/matreshka/issues/2

Fix broken links detected by lychee-action

Use lycheeverse/lychee-action which gives less false positives

Run only once a week and first lint, then link check

Merge pull request #109 from ohenley/add-main-heading

Add main heading and new badge

Add main heading and new badge

This will remove this awesome-lint error:

```
README.md:1:1:   Missing main list heading                                    remark-lint:awesome-heading
```