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.