Adding a "spacemacs mapping" to ease transition from spacemacs to doom

## Background

Doom's existing "spacemacs inspired" keymap is a bit of a double-edged sword. It is close to spacemacs, but different enough that relying on muscle memory will often result in issuing a wrong command.

I took it upon myself to try and recreate the core spacemacs keybindings and combine them where appropriate with doom functionality (if the key wasn't already allocated).

## Question

It doesn't appear that doom has a way to easily distribute the module outside (like spacemacs has with layers).

If that is the case, @hlissner do you think this could be useful to add to the default module or do you have a better idea on how to distribute this as an optional keymap?

## Progress

I am making good headway here if you want to see what the remap looks like:
https://github.com/jsmestad/dfiles/blob/master/.doom.d/%2Bbindings.el#L496-L854