Bump version to 0.21.0; rework changelog, contributors, and docs

Release:
- Bump version to 0.21.0 and regenerate tusb_option.h, library.json,
  repository.yml, sonar-project.properties, boards.rst, dependencies.rst
- Add 0.21.0 release notes and split the changelog into per-release files
  under docs/info/changelog/ (date out of title, driver/class groups as
  sub-headings, DCD & HCD section after Device/Host stacks)

Contributors:
- Credit each release's PR authors in a Contributors section
- Drop the curated contributors page; add MAINTAINERS.rst

Docs:
- Update Code of Conduct to Contributor Covenant 3.0 (keep it in the repo,
  remove it from the built docs)
- Sidebar: add a home entry, rename the group to "Documentation", move
  Changelog into it, add a GitHub Sponsor button, merge external links,
  rename FAQ; hide the inline toctree on the landing page
- Add the make-release skill and update the AGENTS.md release process

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/tusb_option.h b/src/tusb_option.h
index b5457fe8a..b23b37467 100644
--- a/src/tusb_option.h
+++ b/src/tusb_option.h
@@ -30,8 +30,8 @@
 
 // Version is release as major.minor.revision eg 1.0.0
 #define TUSB_VERSION_MAJOR     0
-#define TUSB_VERSION_MINOR     20
-#define TUSB_VERSION_REVISION  1
+#define TUSB_VERSION_MINOR     21
+#define TUSB_VERSION_REVISION  0
 
 #define TUSB_VERSION_NUMBER    (TUSB_VERSION_MAJOR * 10000 + TUSB_VERSION_MINOR * 100 + TUSB_VERSION_REVISION)
 #define TUSB_VERSION_STRING    TU_XSTRING(TUSB_VERSION_MAJOR) "." TU_XSTRING(TUSB_VERSION_MINOR) "." TU_XSTRING(TUSB_VERSION_REVISION)