fish: repaint prompt when jobs change
weechat: only show buffer notifications for messages by default
mutt: remove aerc-style reply bindings
mutt: prefer received dates over sent dates

The sent date (the date in the Date: header) can easily be spoofed and
should therefore be treated as unreliable. The received date, however,
is added by the sending mail servers and is therefore more trustworthy.
msmtp: use implicit TLS
git: update commit alias

Also remove unused 'pull' aliases.
karabiner: map f3-f9 to actual function keys

I never use the media keys for these (Mission Control, Dashboard,
keyboard backlight, rewind, play/pause, and fast forward), so just map
them to the function keys which is more useful.
tmux: fzfurl: don't require DISPLAY
vim: set yaml indent to two spaces
Add -F flag to LESS env var
mbsync: use keychain
mutt: update config

* Remove superfluous comments
* Add, remove, and modify some bindings
* Use a display filter to highlight git diffs
* Use the tmux fzfurl.sh script to find URLs in messages
tmux: update fzfurl script
weechat: remove bitlbee_typing_notice script
fish: prompt: remove trailing space after command duration
fish: fzf: autoload fzf key bindings

Instead of explicitly searching for the fzf key-bindings.fish file in a
hardcoded list of paths, instead just symlink the file into the fish
`functions` directory so that it is autoloaded.

For example, on macOS with MacPorts:

  $ ln -sf /opt/local/share/fzf/shell/key-bindings.fish ~/.config/fish/functions/fzf_key_bindings.fish
vim: fzf: remove runtimepath modification

New solution: symlink the fzf Vim dir on the system into Vim's packpath

For example, on macOS with MacPorts:

  $ mkdir -p ~/.vim/pack/local/start
  $ ln -sf /opt/local/share/fzf/vim ~/.vim/pack/local/start/fzf
git: remove pass-git-helper as credential manager
Revert "Remove msmtp"

This reverts commit 13fd99db38230b744115393d7dc2b22117585067.
fish: show nix-shell in prompt
vim: add vim-nix plugin