Add configuration for smartcd

Saving my bacon setting up environment variables per project so that I
don't have to remember to do it any more.
Add vim-sleuth plugin

Boss likes tabs at tabstops, I like spaces. Some projects go my way,
some projects go his way. Switching configurations is a pain, vim-sleuth
detects the settings that make sense for the current file and uses them.

https://github.com/tpope/vim-sleuth