klinges modifications: vignette updates and mixinglength() arg reorder

[dklinges9]

By playing through the vignette I corrected typos as I went along (making sure that my Americanized English didn't get in the way!)

Second change is similar to pull request on microctools: changing order of arguments when calling mixinglength(). I think I got them all.

[ilyamaclean]

Thanks - now merged