Rename and slightly reword error page

package.yaml

@@ -80,5 +80,5 @@ scripts:
 # Parcel config
 source:
   - src/index.html
-  - src/404.html
+  - src/error.html
 browserslist: '> 1%, not dead'

src/error.html

@@ -2,16 +2,16 @@
   <block name="content">
     <section class="section">
       <div class="container">
-        <h1 class="title has-text-weight-normal">404</h1>
+        <h1 class="title has-text-weight-normal">{{ error.status_code }}</h1>
 
         <div class="columns">
           <div class="column content">
             <!-- prettier-ignore -->
             <markdown>
-              Whatever you were expecting to see here doesn't exist.
+              {{ error.message }}
 
-              If you were sent here from a link and you really think
-              this page *should* exist, feel free to contact me!
+              If you think this is a mistake, feel free to [contact
+              me](~/src/mail.html)!
             </markdown>
           </div>
         </div>