Web: handle query string input line by line

This changes how input from a query string are handled.  Handling them
line by line produces output that more closely resembles how it would
have looked like when typed in interactively.

Note that this is technically a breaking change:  existing numbat.dev
URLs in the wild that contain newlines in the middle of statements will
no longer work.

Closes #205

numbat-wasm/www/index.js

@@ -58,7 +58,7 @@ function interpret(input) {
     output = result.output;
 
     if (!result.is_error) {
-        combined_input += input + "\n";
+        combined_input += input.replace(/\n/g, " ") + "\n";
         updateUrlQuery(combined_input.trim());
     }
   }
@@ -87,7 +87,10 @@ function main() {
     if (location.search) {
       var queryParams = new URLSearchParams(location.search);
       if (queryParams.has("q")) {
-        term.exec(queryParams.get("q"));
+        // feed in the query line by line, as if the user typed it in
+        for (const line of queryParams.get("q").split("\n")) {
+          term.exec(line + "\n");
+        }
       }
     }
   });