Refactor shell setup into ~/.zshenv and ~/.zshrc files

It was time to split the environment related stuff out to ~/.zshenv,
leaving my ~/.zshrc file specifically for setup of interactive shells.

zsh/aliases.zsh

@@ -27,6 +27,20 @@ alias di="colordiff"
 alias devnullsmtp="java -jar $DOTBIN/DevNullSmtp.jar"
 alias open_ports="sudo lsof -i -P | grep --color=never -i \"listen\""
 
+# Homebrew
+if (( $+commands[brew] )); then
+  alias br="brew"
+  alias ca="brew cask"
+  alias cask="brew cask"
+  alias bb="brew bundle"
+  alias bbg="brew bundle --global"
+fi
+
+# Flutter
+if (( $+commands[flutter] )); then
+  alias fl="flutter"
+fi
+
 # Flush DNS cache
 alias flush_dns="dscacheutil -flushcache"