* add internal/diagnostics/state.vim
* add unit tests
* add s:enabled
* clean up diagnostics state during server exit
* remove echom
* add tests for lsp_server_exit
* reset when enable
* add notify function
* add link to diagnostics spec
* add callbag.vim
* add diagnostics
* add comments
* implement cancel
* optimize cancelled=1
* handle more cancel cases
* use callbag for echo.vim
* rename to _enable() _disable() and also check for changedtick
* move to internal
* group lsp#request
* ignore terminal for echo
* dont bother to subscribe if diagnostics echo not enabled
* remove deprecation comment
* update callbag.vim to v0.1.0
* fix lint issues