Upgrade eleventy to 2.0.0-beta

[SleeplessByte]

Eleventy 11 comes with --incremental build support, as well as other plugins. This is a pre-requisite for #131 and #135.

Fixes #138

I believe this is the minimum requirement to make the jump from 1.x to 2.x. According to the upgrade helper we've passed all the deprecations:

• PASSED Eleventy has a new default ignore pattern of **/node_modules/** (previously: node_modules/**). Read more, including how to revert this behavior: https://www.11ty.dev/docs/ignores/#node_modules. This does not appear to affect your project, as you have no nested node_modules folders!
• PASSED This project is using Node 14 or newer!
• PASSED This project is not using the Render plugin. If it did, I’d remind you that the renderTemplate shortcode behavior changed slightly in 2.0. But you don’t need to worry about it here. Read more: Render Plugin default template language should inherit the parent page syntax 11ty/eleventy#2310
• PASSED eleventyConfig.ignores are no longer re-used for the file watcher during --watch and --serve. If you’d like files to be ignored by the file watcher (to avoid triggering new builds), use the new dedicated eleventyConfig.watchIgnores API instead. This project doesn’t seem to be making use of the feature. Read more: https://www.11ty.dev/docs/watch-serve/#ignore-watching-files
• PASSED Browsersync is no longer the default Development Server in Eleventy. This project doesn’t seem to be making use of any custom Browsersync options, so it’s unlikely to be affected! Learn more: https://www.11ty.dev/docs/dev-server/
• PASSED Global data files with one or more dots in the file name are stored differently in the data cascade in Eleventy 2.0. For example, a.b.json stores as 'a.b': value instead of a: { b: value }. This project has no affected data file paths. Read more: Fix #1242 Dot Pathing in data file paths 11ty/eleventy#1912
• PASSED This project is not using the removed renderData feature. Read more about renderData: Removing deprecated renderData feature. 11ty/eleventy#2356
• PASSED When calculating page.fileSlug dates are now stripped from parent folder names of index.* files. This project has no file/directory paths that are affected, no worries here. Read more: Strip date from directory slugs when calculating page.fileSlug 11ty/eleventy#2111