* Fix various doc, user-facing, and source comment typos Found via `codespell -q 3 -S ./options/locale,./vendor -L ba,pullrequest,pullrequests,readby`
* add migrations * fix package dependency * fix lints * implements migrations except pull requests * add releases * migrating releases * fix bug * fix lint * fix migrate releases * fix tests * add rollback * pull request migtations * fix import * fix go module vendor * add tests for upload to gitea * more migrate options * fix swagger-check * fix misspell * add options on migration UI * fix log error * improve UI options on migrating * add support for username password when migrating from github * fix tests * remove comments and fix migrate limitation * improve error handles * migrate API will also support migrate milestones/labels/issues/pulls/releases * fix tests and remove unused codes * add DownloaderFactory and docs about how to create a new Downloader * fix misspell * fix migration docs * Add hints about migrate options on migration page * fix tests