Bug fixes

923d581 Improved error reporting in hdl_files.go, simplified getAPIKey().
683c005 fix: misleading comment in plugins config.
dd23f4e fix build script: GOPATH is not needed when using go-mod.
d6f3650 Encode email subject as quoted-printable.
a3c8c40 fix: link uploaded avatar to topic for new topics.
0769754 Update fix-typos.yml.
1b277e2 lint warnings fixed.
6acd635 Silence message edit notifications.