* import docs into main repository

Signed-off-by: Matti Ranta <matti@mdranta.net>

* switch gitter to discord for drone.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* add event

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* only notify build fail message.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

That is annoying on Windows, since the editor will change the file if
you just open it. Git will checking as LF anyway.

We are using gofmt to format our code. This will emit tabs.
The standard is tabs which is 8 spaces.

- Refactor code to use sync.UniqueQueue
- Closes #3509

[CI SKIP]