Returning exit code 3 when no version is found.
Consistently returning exit code 1 when version is not installed yet.
Return the exit code of `nvm use` when `nvm install`-ing.
Removing reference to NVM_PROFILE in README. Fixes #442
Silently support `nvm i x.x.x`. Fixes #443.
Making sure there's test coverage for `nvm i`
Use "typeset" instead of "local" for portability