Set up OS-specific zsh configs

- Move keybinds into a match for Darwin systems
- Move BSD-isms into the same match, split off Linux-isms for binutils
  into a match for linux systems
- Add a comment or two for some directives I did not immediately
  remember what they did, so I'll remember next time more easily

.zshrc

@@ -1,5 +1,6 @@
 export LANG=en_US.UTF-8
 
+# Start keychain only on my personal system
 if [ -n "$SSH_CLIENT" ] || [ -n "$SSH_TTY" ]; then
     SESSION_TYPE=ssh
 else
@@ -15,11 +16,6 @@ fi
 
 source ~/.p10k/powerlevel10k.zsh-theme
 
-# Make extra keys in MacOSX behave like expected
-bindkey "^[[H" beginning-of-line  # HOME
-bindkey "^[[F" end-of-line        # END
-bindkey "^[[3~" delete-char       # DEL
-
 # Print user@host into title so terminal tabs are correct
 # Despite being called precmd() this executes after process exits, before prompt
 precmd() { echo -ne "\033]0;${USER}@${HOST}\007" }
@@ -34,17 +30,30 @@ if [[ -a /usr/bin/most ]]; then
     export PAGER=most
 fi
 
+# OS-specific directives
+case "$OSTYPE" in
+  darwin*)
+    bindkey "^[[H" beginning-of-line  # HOME
+    bindkey "^[[F" end-of-line        # END
+    bindkey "^[[3~" delete-char       # DEL
+    alias ls='ls -G'
+  ;;
+  linux*)
+    alias ls='ls --color=auto'
+    alias diff='diff --color=auto'
+  ;;
+esac
+
+# Global aliases
+alias ct="clear && task"
+alias tt="taskwarrior-tui"
+alias grep='grep -EIs --color=auto --exclude-dir=.git'
+
 HISTFILE=~/.zsh_history
 HISTSIZE=10000
 SAVEHIST=10000
 setopt appendhistory
 
-alias ct="clear && task"
-alias tt="taskwarrior-tui"
-alias ls='ls --color=auto'
-alias grep='grep -EIs --color=auto --exclude-dir=.git'
-alias diff='diff --color=auto'
-
 # Case-insensetive tab completion
 zstyle ':completion:*' matcher-list 'm:{a-z}={A-Za-z}'