Add `elnode--rfc1123-date' and `elnode--file-modified-time'. Add Last-Modified header in `elnode-send-file'.
Add `elnode--rfc1123-date' and `elnode--file-modified-time'. Add Last-Modified header in `elnode-send-file'.
Merge pull request #60 from mathiasdahl/master

Addition of Last-Modified header to elnode-send-file to get caching to work in browsers