handle quotes in Content-Disposition filenames

Summary:
The HTTP standard specifies
(http://www.w3.org/Protocols/rfc2616/rfc2616-sec19.html#sec19.5.1) that
`Content-Disposition` filenames can be quoted. I forgot to handle that.

Closes https://github.com/buildinspace/peru/issues/70.

Test Plan: Add a couple extra cases to the existing test.

Reviewers: sean

Reviewed By: sean

Differential Revision: https://phabricator.buildinspace.com/D144