Add option to preserve whitespace and prevent nunjucks engine from collapsing

[palewire]

There are circumstances, like 1920s modernist poetry, for example, where preserving the whitespace of the HTML is necessary.

I propose some kind of baker.config setting or other environment variable that can globally switch off the hardcoded configuration found here.

I doubt this would be difficult, but I can imagine several different ways to implement it. I'm happy to take a stab at the patch, but I wanted to ask beforehand in case you had opinions on the proper route to take.

[palewire]

This is done.