narray 0.4.0

API changes

• Package no longer depends on abind, pryr
• along=-1 uses last dimension in flatten, subset (#6)
• summarize is kept as translate
• construct no longer allows value aggregation; do this on the data.frame
  before (related to #11)

New functionality

• stack now also accepts multiple arrays as arguments
• construct now has name_axes option to keep column names (#12)
• new lambda syntax (#14)

Bugfix

• map subsets that are NA are dropped with a warning (#13)
• map subsets throw error if not same length as array axis