Motivation for this change

Changelog [1]:

New features
- core: use getopt to parse command line arguments
- core: add option weechat.look.prefix_same_nick_middle
- core: add option weechat.look.buffer_time_same
- core: use seconds by default in /repeat interval, allow unit for the interval
- core: allow text in addition to a command in command /repeat
- core: add option "addreplace" in command /filter
- api: return allocated string in hook_info callback and function info_get
- api: replace argument "keep_eol" by "flags" in function string_split
- api: add function command_options
- api: add function string_match_list
- irc: add bar items "irc_nick", "irc_host" and "irc_nick_host"
- irc: add variable "host" in server structure
- relay: add support of UNIX socket
- relay: add option relay.weechat.commands
- script: use SHA-512 instead of MD5 for script checksum
- spell: rename aspell plugin to spell
- trigger: add hooks "info" and "info_hashtable"
- xfer: rename option xfer.network.speed_limit to xfer.network.speed_limit_send, add option xfer.network.speed_limit_recv

Bug fixes
- core: don’t execute command scheduled by /repeat and /wait if the buffer does not exist any more
- core: set max length to 4096 for /secure passphrase
- core: refilter only affected buffers on filter change
- fset: fix slow refresh of fset buffer during /reload
- irc: fix parsing of MODE command when there are colons after the first mode argument
- irc: fix memory leak in infos "irc_server_isupport" and "irc_server_isupport_value"
- irc: fix length of string for SHA-512, SHA-256 and SHA-1 in help on ssl_fingerprint option
- irc: display an error with /allchan -current or /allpv -current if the current buffer is not an irc buffer
- irc: fix update of channels modes with arguments when joining a channel
- irc: quote NICK command argument sent to the server
- php: fix memory leak in functions string_eval_expression, string_eval_path_home, key_bind, hook_process_hashtable, hook_hsignal_send, info_get_hashtable, hdata_update
- relay: fix crash when a weechat relay client reloads the relay plugin with /plugin reload relay
- spell: fix detection of nick followed by the nick completer
- trigger: fix split of hook arguments

Tests
- unit: add tests on function util_signal_search

Build
- core: fix value of libdir in file weechat.pc
- core: fix generation of man page weechat-headless with autotools
- core: add CMake option "ENABLE_CODE_COVERAGE" to compile with code coverage options (CMake ≥ 3.0 is now required)
- core: fix compilation on Mac OS
- lua: add detection of Lua 5.3 with autotools
- ruby: add detection of Ruby 2.6
- tests: fix compilation of tests on FreeBSD

[1] https://weechat.org/files/changelog/ChangeLog-2.5.html#v2.5

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nix-review --run "nix-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Assured whether relevant documentation is up to date
• Fits CONTRIBUTING.md.