Automate switching between day/night color schemes

This sets up individual light and dark color scheme files for vim/neovim
and alacritty, adds a script (`set-color`) for placing them, and
includes two no-arg scripts for later keybinding (`day-mode` and
`night-mode`).

Thanks to this blog post for the idea to `cat` the YAML into place:
https://shuheikagawa.com/blog/2020/02/14/switching-colorschemes-of-vim-and-alacritty/

TIL YAML is concatenative!

zsh/.zshrc

@@ -32,12 +32,12 @@ zle -N edit-command-line
 bindkey '^x^e' edit-command-line
 
 if [[ $TERM =~ '256color' ]]; then
-    local blue="%F{81}"
-    local orange="%F{166}"
-    local purple="%F{135}"
-    local red="%F{196}"
-    local green="%F{118}"
-    local gray="%F{241}"
+    local blue="%F{12}"
+    local orange="%F{11}"
+    local purple="%F{13}"
+    local red="%F{9}"
+    local green="%F{10}"
+    local gray="%F{7}"
 else
     local blue="%{$fg[cyan]%}"
     local orange="%{$fg[yellow]%}"