Try out Space as my leader

Reaching up to \ feels a bit too far so I want to try something closer
to home. I'm not sure how I feel about using my thumbs or the extra
force required for Space, but we'll see how it goes.

It's certainly very confusing at first.

Moved \ to folding (which Space used to do).
\ is too clumsy for folds; use <Leader>l instead

I usually navigate up and down through code using jk and fold to get
stuff out of my way. Jumping up to \ is too far, so use <Leader>l
instead. l is move right which often opens folds up anyway.
Prevent accidental \ usage

Until I get accustomed to \ as my leader, I need to warn myself when I
use it incorrectly.

After that, maybe I can use it as LocalLeader.
Map <Leader>v; to <Leader>v:

; is much easier to hit than :
Make Space do nothing after timeoutlen

Space is my leader, but it still moves forward a character after
timeoutlen. Prevent that so it only represents leadership.
Super power my : leader map

: is often used so the map makes sense, but lets try using the cmdwin
for it too.