Incremental build for markdown files

[magua-io]

Is your feature request related to a problem? Please describe.
Minor modification on a single markdown file takes the whole build time to reload. The more pages I have, the longer it takes.

Describe the solution you'd like
Incremental build support for markdown files. Fast reloading should happen after saving the markdown file.

Describe alternatives you've considered
N/A

Additional context
I have two repos are using Eleventy as the SSG to generate documentation pages. The first one contains around 20 pages, and each rebuild time is around 25 seconds. The second one contains 180+ markdown files, and each rebuild time is around 160 seconds.

[zachleat]

Duplicate of #108 and #2022