Feat: New theme named tomorrow_night that uses tomorrow-night-like styling that was the default when base16-nvim plugin not found

[cartercanedy]

Requested feature

I propose a new builtin theme that simply uses the default base16 colors that already exist within the base16 theme file without trying to load other base16 nvim plugins

Motivation

I was messing around with my lualine config, and I realized that I really liked the base16 default colors, a lot. I'm just annoyed by the fact that I get a warning notice on starting up nvim saying that I don't have a base16 plugin on runtimepath.