New Features

Actually removal of features:
- No longer an escript
- Functionality that is a duplicate of rebar3 has been removed
- rebar3 is now able to pass a map of OTP Applications so relx does not need to do a discovery step
- Releases are no longer discovered unless needed
Add support for exref, {exref, [Apps]} and src_tests
- Neither form of exref will work if using rebar3 as an escript. Install with rebar3 local install in order to use this feature.
Add support for multiple mode types:
- dev: Same as the old dev_mode option. Creates symlinks for applications and configuration.
- minimal: Same as prod but does not include ERTS in the release.
- prod: Strips debug info from beam modules, includes ERTS and excludes src
Extended start script no longer requires exact version of ERTS but attempts to use the one in the PATH if none is bundled in release
On OTP-23:
- extended start script will use erl_call instead of nodetool
- remote shell will not bind to a listen port making use of epmdless simpler

New Defaults

extended_start_script is true by
Automatically includes config/sys.config[.src] and config/vm.args[.src]
- set {sys_config, false} and {vm_args, false} to force them to be left out
Release boot script is now always named start.boot

eval requires trailing period: bin/<release_script> eval "3."
rpcterms removed
rpc takes list of arguments, so to call foo:bar(1,2,3): bin/<release_script> foo bar "[1,2,3]."
start renamed to daemon
- attach renamed to daemon_attach
remote_console has aliases remote and remsh