polyglot update + new search-upwards package

[Sage Gerard]

Giving away some more code.

• polyglot is now version 1.0. Includes a new functional workflow where Markdown+Racket pages can replace themselves entirely [1]. The public API now includes the means to evaluate Racket modules stored in tagged x-expressions (Thanks to Paulo Matos for the suggestion). I'm really excited about where this project is going!
  
• New package: search-upward [2]. The use case is finding specialized rcfiles or directories like `node_modules` while walking towards the root directory.
  

[1]: https://docs.racket-lang.org/polyglot/functional-workflow.html?q=polyglot

[2]: https://pkgd.racket-lang.org/pkgn/package/search-upward

~slg