format code with fish_indent

support serverless.yml

use short flags

erase exported nvm_current_version before autoload nvm

Update README.md

delay nvm until first fish_prompt in interactive mode, support non-interactive mode

do not invoke nvm unless we're interactive

fix: run nvm on load

autoload nvm on start

fix switching to non-installed version

use `nvm use' for perf

Create README.md

upgrate to nvm@2, fisher@4

use fishfile to install dependencies

use universal scope when run `nvm use` directly