Add a basic indexing/search test

cmd/sitesearch/sitesearch_test.go

cmd/sitesearch/testdata/markdown/about.ca.md

cmd/sitesearch/testdata/markdown/about.de.md

cmd/sitesearch/testdata/markdown/about.en.md

cmd/sitesearch/testdata/markdown/about.es.md

cmd/sitesearch/testdata/markdown/about.fr.md

cmd/sitesearch/testdata/markdown/about.it.md

cmd/sitesearch/testdata/public/all_pages.json