feat(plugin): adds content plugin

[stalniy]

Awesome Contribution Checklist:

• [x] I have read, and re-read the Contributing Guidelines
• [x] I have searched to ensure the suggested item doesn't exist on this list
• [x] This PR contains only one item

Please Provide a Link A Repository for Your Addition

https://github.com/stalniy/rollup-plugin-content

Please Describe Your Addition

This plugins allows to build custom static websites without efforts. It generates JSON assets out of specified folders which later can be fetched by UI to render a page. It supports plugins to additionally generate "summaries" (lists of pages) for specific categories or tags. This allows to use it to create an offline search index for client side full text search

P.S.: doesn't have tests for now but used to generate documentation for my project. Please check the Example section.

[shellscape]

Please add tests with comprehensive coverage and we'll consider this addition. Not until then, however.

[shellscape]

Closing due to lack of tests.