Make the home page's AS name search work (closes #151)

The AS Name Search card on the home page said the search was coming
soon. It now asks the new GET /api/v1/search/as?q=<text>, which
searches the AS list built into asinfo, and lists the matches as links
to their AS pages. An empty q answers 400. asinfo.Search now ignores
case and returns its matches in AS number order.

A match can be an AS that the database does not hold yet. Its AS page
and /api/v1/as/{asn} now answer with its handle and description from
asinfo and no prefixes, instead of 404. Empty prefix lists in that JSON
answer are [] rather than null.

Model: opus-5-5

pkg/asinfo/doc.go

@@ -16,8 +16,9 @@ Basic usage:
 	// Get just the description
 	desc := asinfo.GetDescription(15169) // "Google LLC"
 
-	// Search for AS entries
-	results := asinfo.Search("University")
+	// Search the handles and descriptions, ignoring case; the matches come
+	// in AS number order
+	results := asinfo.Search("university")
 	for _, as := range results {
 		fmt.Printf("AS%d: %s\n", as.ASN, as.Description)
 	}