rebar.config.script that checks for maps support in the release rebar
  is using to compile. hopefully this is the same release as the
  artifact is being run on
add a check for env var to optionally compile without support for
  erlang maps
switch to feature detection rather than trying to figure out from
  compiler version/release whether maps should be supported
correctly pass compile opts to rebar
refactor out copy/pasted encode methods
fix rebar.config.script for < otp 17.0
add a rebar.config option to disable maps
remove mention of internal state manipulation from CHANGES, leave
  experimental for now
update README and CHANGES with details for 2.0
minor refactoring of feature detection
v2.0