improve file selection button, first version of uw8-tool to build base.wasm

web/src/index.html

@@ -12,8 +12,7 @@
         <div id="centered">
             <canvas id="screen" width="640" height="512"></canvas>
             <div id="message"></div>
-            <button onclick="document.getElementById('cart').click()">Load cart...</button>
-            <input id="cart" style="visibility: hidden" type="file" accept=".wasm,.uw8,application/wasm">
+            <button id="cartButton">Load cart...</button>
         </div>
         <div id="footer">
             <a href="http://unlicense.org/" ref="license">Unlicense</a>