Vignette and small fixes

New features

• There is a vignette vignette("alluvial", package="alluvial") illustrating basic usage of alluvial(). The vignette needs dplyr package so it is now Suggested.

Minor updates

• README has been updated. It is dynamically generated from an associated .Rmd file. Some typos fixed.

v0.1-1

Available on CRAN