context delegates: response.lastModified and response.etag

only doing setters because i think getters would be pretty confusing.

docs/api/context.md

@@ -62,6 +62,8 @@
   - `ctx.redirect()`
   - `ctx.attachment()`
   - `ctx.set()`
+  - `ctx.lastModified=`
+  - `ctx.etag=`
 
 ## API
 

lib/context.js

@@ -379,6 +379,22 @@ module.exports = {
     return this.request.type;
   },
 
+  /**
+   * Delegate to Response#lastModified=.
+   */
+
+  set lastModified(val) {
+    this.response.lastModified = val;
+  },
+
+  /**
+   * Delegate to Response#etag=.
+   */
+
+  set etag(val) {
+    this.response.etag = val;
+  },
+
   /**
    * Delegate to Request#accepts().
    */