Mercurial 4.0 release

Features

The following commands now also have experimental formatter support: 'hg version', 'hg grep' and 'hg config'
New template keywords and functions: termwidth, mod(a, b), relpath(path)
Basic arithmetic operations in template such as termwidth - 10
follow() revset takes new startrev parameter
Bash completion now allows skipping potentially expensive status call for completing 'hg status' arguments, using $HGCOMPLETE_NOSTATUS environment variable

A number of changes were made to move and copy tracking, to make sure move and copy information is not lost during commands like 'hg graft'
Compound revset expression is now properly ordered
Performance of client-side application of bundle data for generaldelta repos has been significantly improved. This makes 'hg clone', 'hg pull', and 'hg unbundle' operations faster. Cloning the Firefox repository now consumes 70+s less CPU time and completes over a minute faster (when not network or I/O bound).
The storage and transfer of changeset data has been optimized to improve read performance
Python 3 support has received a lot of improvements (but will take a lot of additional work)
zlib performance in hgweb is improved, and it's now possible to control zlib compression level using server.zliblevel option
Various improvements for largefiles extension related to executable bit tracking and removing files, better recovery from an interrupted state

A full overview is available on WhatsNew.