zsh: Divide zshrc into zshrc.d

Move every file from plugins into zshrc.d as well as all bigger blobs in
the zshrc into their own files there.
Some stuff is still in there that I am not all too sure where it
belongs. TODO: Move.

Because all external plugins are now sourced over a symlink I had to
create a fork of fzf-tab for now that supports that.
See: https://github.com/Aloxaf/fzf-tab/pull/153

.config/zsh/zshrc.d/50-external-plugins/35-syntax-highlighting.theme

@@ -0,0 +1,30 @@
+ZSH_HIGHLIGHT_HIGHLIGHTERS=(main brackets)
+## colors: 0-7 standard, 8-15 high-intensity
+
+## red
+ZSH_HIGHLIGHT_STYLES[bracket-error]='fg=009,bold'
+ZSH_HIGHLIGHT_STYLES[unknown-token]='fg=009,bold'
+## green
+ZSH_HIGHLIGHT_STYLES[arg0]='fg=076'
+ZSH_HIGHLIGHT_STYLES[suffix-alias]='fg=076,underline'
+ZSH_HIGHLIGHT_STYLES[bracket-level-2]='fg=076,bold'
+ZSH_HIGHLIGHT_STYLES[precommand]='fg=076,underline'
+## blue
+ZSH_HIGHLIGHT_STYLES[bracket-level-1]='fg=012,bold'
+## yellow
+ZSH_HIGHLIGHT_STYLES[double-quoted-argument]='fg=011'
+ZSH_HIGHLIGHT_STYLES[dollar-quoted-argument]='fg=011'
+ZSH_HIGHLIGHT_STYLES[bracket-level-4]='fg=011,bold'
+ZSH_HIGHLIGHT_STYLES[single-quoted-argument]='fg=011'
+ZSH_HIGHLIGHT_STYLES[reserved-word]='fg=011'
+ZSH_HIGHLIGHT_STYLES[path_prefix]='fg=011,underline'
+## cyan
+ZSH_HIGHLIGHT_STYLES[dollar-double-quoted-argument]='fg=014'
+ZSH_HIGHLIGHT_STYLES[back-double-quoted-argument]='fg=014'
+ZSH_HIGHLIGHT_STYLES[back-dollar-quoted-argument]='fg=014'
+ZSH_HIGHLIGHT_STYLES[bracket-level-5]='fg=014,bold'
+ZSH_HIGHLIGHT_STYLES[rc-quote]='fg=014'
+## black/dark grey
+ZSH_HIGHLIGHT_STYLES[comment]='fg=008,bold'
+## magenta
+ZSH_HIGHLIGHT_STYLES[bracket-level-3]='fg=13,bold'