Notable new features

A new os: module providing access to operating system functionality.
A new read-bytes command for reading a fixed number of bytes.
New commands in the file: module: file:open-output, file:seek and file:tell.
Maps now have their keys sorted when printed.
The peach command now has a &num-workers option (#648).
The from-json command now supports integers of arbitrary precision, and outputs them as exact integers rather than inexact floats.
A new str:fields command (#1689).
The order and compare commands now support a &total option, which allows sorting and comparing values of mixed types.
The language server now supports showing the documentation of builtin functions and variables on hover (#1684).
Elvish now respects the NO_COLOR environment variable. Builtin UI elements as well as styled texts will no have colors if it is set and non-empty.

Notable bugfixes

has-value $li $v now works correctly when $li is a list and $v is a composite value, like a map or a list.
A bug with how the hash code of a map was computed could lead to unexpected results when using maps as map keys; it has now been fixed.

The except keyword in the try command was deprecated since 0.18.0 and is now removed. Use catch instead.
The float64 command was deprecated since 0.16.0 and emitted deprecation warnings since 0.19.1, and is now removed. Use num or inexact-num instead.

Deprecated features will be removed in 0.21.0.

The following deprecated features trigger a warning whenever the code is parsed and compiled, even if it is not executed: