[website] Make top-level menu URLs

[plroebuck]

Make the 'Assertions' top-level URL bookmarkable.
http://unexpected.js.org/assertions/ doesn't exist; menu button click autoroutes to http://unexpected.js.org/assertions/any/to-be/.

Make the 'API' top-level URL bookmarkable.
http://unexpected.js.org/api/ doesn't exist; menu button click autoroutes to http://unexpected.js.org/api/addAssertion/.

Inconsistent with 'Plugins', which does exist, though its sections lack anchors and cannot be jumped to directly (e.g., http://unexpected.js.org/plugins/#install)

[sunesimonsen]

http://unexpected.js.org/assertions/ doesn't currently exists, what should be on that url?

[plroebuck]

Any generic "index.html" that includes the left-hand list of all possibles. Right-hand content for Assertions page might contain generalities and a list of the assertion groups. Right-hand content for API page could give generic concepts, overalls thoughts, and example usage.

This logic should probably also be applied to each of the assertion groupings as well; these could have right-hand content explaining anything that was common to the grouping.

[alexjeffburke]

I’ve had a quick look at this - it requires patching the documentation generator (partially done) to allow an assertions.md file to override the generated menu option plus retain a sidemenu listing down the left - then a file being added with something to the docs directory in core.