Split vignettes logically and add other contextual vignettes

[mstackhouse]

          > And any thoughts on documentation updates to make this more clear?

I'll need to do a review here, but since there's only one vignette, I think we probably want to split vignettes out to outline different potential configurations. For example:

• Using envsetup for single path environments
• Using envsetup for hierarchical path environments
• A vignette around reading and writing data
• A vignette around using functions stored in autos paths

Another thing I think could be more clear is when is the right time to call library(envsetup). I think I created an infinite loop in an Rprofile I was working with yesterday, because it crashed my R session every time I restarted. I didn't have time to pinpoint the issue though - and this was with calling envsetup in the .RProfile itself.

Originally posted by @mstackhouse in #10 (comment)