Improve licensing information (#1298)

Add license details on a per-file basis for internal docs using the SPDX
license ID standard [1]. This is in line with the existing practice of
defining explicitly the applicable license for all source code (such as
scripts and tests) as well as external facing docs on the file level.

Also use SPDX license IDs[1] for external facing docs as a way of having
a standardized license declaration for these files (in addition to the
human-readable declaration in the documentation file footers).

Correspondlgy, expand the "License" section in README with more detail
regarding both "supporting code" as well as the fact that individual
files have their license declared in banner comments.

Lastly, use SPDX license IDs [1] for git hook scripts as well and add a
missing banner comment (with license info) to `testing.d.ts`.

--
1. https://spdx.dev/learn/handling-license-info/

CHANGELOG.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC0-1.0 -->
+
 # Changelog
 
 All notable changes to _Shescape_ will be documented in this file.

CONTRIBUTING.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC0-1.0 -->
+
 # Contributing Guidelines
 
 The _Shescape_ project welcomes contributions and corrections of all forms. This

README.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
+
 # Shescape
 
 [![GitHub Actions][ci-image]][ci-url]
@@ -78,6 +80,13 @@ The source code is licensed under the `MPL-2.0` license, see [LICENSE] for
 the full license text. The documentation text is licensed under [CC BY-SA 4.0];
 code snippets under the [MIT license].
 
+Supporting code, such a scripts and tests, is generally licensed under the `MIT`
+license. However, individual files may be licensed differently depending on the
+intend or origin.
+
+The license under which a given file is available can always be found in the
+file's banner comment.
+
 [ci-url]: https://github.com/ericcornelissen/shescape/actions/workflows/checks.yml
 [ci-image]: https://github.com/ericcornelissen/shescape/actions/workflows/checks.yml/badge.svg
 [coverage-url]: https://codecov.io/gh/ericcornelissen/shescape

RELEASE.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC0-1.0 -->
+
 # Release Guidelines
 
 If you need to release a new version of _Shescape_, follow the guidelines found

SECURITY.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC0-1.0 -->
+
 # Security Policy
 
 The maintainers of the _Shescape_ project take security issues seriously. We

docs/api.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
+
 # Shescape API
 
 This document provides a description of the full Application Programming

docs/recipes.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
+
 # Shescape Recipes
 
 This document provides examples, called _recipes_, for how to use Shescape in

docs/testing.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
+
 # Testing with Shescape
 
 This document provides an overview of why and how to use Shescape's testing

docs/tips.md

@@ -1,3 +1,5 @@
+<!-- SPDX-License-Identifier: CC-BY-SA-4.0 -->
+
 # Tips
 
 This document provides tips to avoid shell injection beyond using a shell

script/hooks/common.sh

@@ -1,4 +1,5 @@
 #!/bin/sh
+# SPDX-License-Identifier: MIT
 
 get_stash_count () {
   readonly count="$(git rev-list --walk-reflogs --count refs/stash 2> /dev/null)"

script/hooks/pre-commit

@@ -1,4 +1,6 @@
 #!/bin/sh
+# SPDX-License-Identifier: MIT
+
 . "$(dirname "$0")/_/husky.sh"
 . "$(dirname "$0")/common.sh"
 

script/hooks/pre-push

@@ -1,4 +1,6 @@
 #!/bin/sh
+# SPDX-License-Identifier: MIT
+
 . "$(dirname "$0")/_/husky.sh"
 . "$(dirname "$0")/common.sh"
 

testing.d.ts

@@ -1,3 +1,8 @@
+/**
+ * @overview Contains TypeScript type definitions for shescape/testing.
+ * @license MPL-2.0
+ */
+
 import type { Shescape as ShescapeType } from "shescape";
 
 /**