allow auto features to be disabled without restarting Vim

[bhcleek]

I find sometimes want to change the settings of vim-go that control whether or not some actions happen in response to events (e.g. formatting, linting, etc.). This change allows the settings to be changed at runtime instead of having to restart Vim to pick up the changes.

There were a couple of autocmd entries where I removed the nested argument, because it didn't seem to be necessary.

[fatih]

Thanks @bhcleek 👍