(test) New tests, to server default & non-default files
Merge pull request #42 from tarcieri/use-path-extensions

use std::io::fs::PathExtensions
Merge pull request #39 from Valve/test/add-basic-tests

(test) first tests, more will follow
(fix) Error::abstract was renamed to erase
(fix) Return 404, if file not found

Closes #40.
(cleanup) Remove unused code
(fix) Don't send 404 response without body

Without the body, the user just sees a blank page, which isn't very
friendly. Ideally, I think we'd want a customizable 404 page, but this
is better than nothing.