Merge pull request #2 from s-u/key-aware-chunk-reader

Key aware chunk reader
update docs
handle map-identity better; allow two options
de-strialize stream before checking FUN or else it's always pass-thru
adding c.hinput to combine hinput objects
functionality for numeric mstrsplit
adding support for numeric mstrsplit with raw vector
Merge branch 'master' into key-aware-chunk-reader