activate on all files matching *.slides.*

We don't actually do anything special for *.slide.hs, and the
ftplugin and autocmd work just find with a wildcard at the end, so
let's just not care about the filetype.
Merge pull request #2 from frasertweedale/baby-steps

activate on all files matching *.slides.*
Fixes escape code propagation from haskell slide configurators. Fixes styles location on mac.