Re-organize the shells' initialization logic

- unify ~/.config/shell/aliases.sh and ~/.config/shell/utils.sh
  into a common ~/.config/shell/init.sh
- split the contents of ~/.config/shell/aliases.sh
  into the folder ~/.config/shell/aliases.d
- split the contents of ~/.config/shell/utils.sh
  into the folder ~/.config/shell/utils.d

.config/shell/aliases.d/generic.sh

@@ -0,0 +1,67 @@
+# Generic shell aliases for bash and zsh
+
+
+_command_exists() {
+    command -v "$1" 1>/dev/null 2>&1
+}
+
+_in_zsh() {
+    [ -n "$ZSH_VERSION" ]
+}
+
+
+# Re-run last command with sudo privileges
+if _in_zsh; then
+    alias ,,='sudo $(fc -ln -1)'
+else
+    alias ,,='sudo $(history -p !!)'
+fi
+
+
+# Convenient piping with zsh
+if _in_zsh; then
+    alias -g B='| bat'
+    alias -g F='| fzf'
+    alias -g G='| grep'
+    alias -g H='| head'
+    alias -g L='| less'
+    alias -g T='| tail'
+    alias -g NE='2 > /dev/null'
+    alias -g NUL='> /dev/null 2>&1'
+fi
+
+
+# (Non-)obvious synonyms
+alias cls='clear'
+alias help='man'
+
+
+# Various one-line utilities
+alias datetime='date +"%Y-%m-%d %H:%M:%S %z (%Z)"'
+alias datetime-iso='date --iso-8601=seconds'
+alias dotfiles='git --git-dir=$HOME/.dotfiles/ --work-tree=$HOME'
+alias external-ip="curl https://icanhazip.com"
+alias external-ip-alt="curl https://ipinfo.io/ip\?token=cfd78a97e15ebf && echo"
+alias external-ip-extended-infos="curl https://ipinfo.io/json\?token=cfd78a97e15ebf && echo"
+alias speedtest="curl -s https://raw.githubusercontent.com/sivel/speedtest-cli/22210ca35228f0bbcef75a7c14587c4ecb875ab4/speedtest.py | python -"
+
+
+# Fix common typos
+_command_exists ifconfig && alias ipconfig='ifconfig'
+_command_exists R && alias r='R'
+
+
+# Use sane defaults
+_command_exists exa && alias exa='exa --group-directories-first --git --time-style=long-iso'
+_command_exists netstat && alias ports='netstat -tulanp'
+_command_exists screenfetch && alias screenfetch='screenfetch -n'
+alias uptime='uptime --pretty'
+alias wget='wget --continue'
+
+
+# Create shorter aliases for various utilities
+_command_exists batcat && alias bat='batcat'
+_command_exists fdfind && alias fd='fdfind'
+_command_exists neofetch && alias nf='neofetch'
+_command_exists ranger && alias rn='ranger'
+_command_exists screenfetch && alias sf='screenfetch'