Use nimsuggest instead of nim idetool

[bkerin]

Ok hopefully this is right pull request this time.

The g:nim_project_file is a bit of a hack but otherwise this is a decent start towards using nimsuggest rather than nim idetools (which doesn't seem to exist in my most recent copy of nim and araq confirmed on irc that nimsuggest is the new way).

[brentp]

+1 would be nice to have this as the default. I don't have nim idetools either.