Version 0.2.0

• Added joining verbs and a corresponding vignette describing them (#1).
• Added the distinct verb.
• transmute is no longer an alias for select. This is to make the latter more flexible in some
  bare selection cases (like combining several tidyselect calls), and leave the former more simple
  and preferable for actual transmutation cases (#4).
• Both mutate_sd and transmute_sd now support a list of functions as input, but with slightly
  different semantics; check the vignette (#8 and #11).
• Now both mutate_sd and filter_sd support the .COL pronoun for .SDcols predicates, but they
  remain eager in this regard.
• select and filter_on gained a .negate parameter (#9 and #6).
• mutate gained a .sequential parameter to enable usage of newly created columns.
• Added some debugging statements when option table.express.verbose is TRUE, or
  .verbose = TRUE in start_expr/chain.
• Updates to main vignette.
• Semi-breaking change: *_sd verbs now have .SDcols before their ellipsis. This should only
  require code adjustment for transmute_sd when .SDcols was left missing.