shell/base16shell, zsh_xtheme: change message text.
zshrc: add check or git clone logic for antigen.
shell/base16shell: use MDX_BASE_COLOR to store current colorscheme.
shell/zsh_xtheme: use MDX_ZSH_THEME to store current zsh theme.
zshrc: add mdxinfo() to show some info (e.g. zsh theme, colorscheme, etc.)