Faster boosting time if no changes happen since last build.

[magua-io]

Is your feature request related to a problem? Please describe.
No matter whether any files got changed or not, Eleventy always tries to perform "writing templates" to serve the pages.

Describe the solution you'd like
I hope there is way to start the server faster without writing templates if possible. Maybe just serve with the cache.

Describe alternatives you've considered
N/A

Additional context
N/A

[zachleat]

Duplicate of #108, specifically this is requesting cold-start incremental