Multiple enclosures in one item

This is better, since 'addEnclosure' means 'add one *more* enclosure'.

* setEnclosure: Expects an integer for length parameter greather than zero.
* setAuthor: email parameter is also used in RSS2 feeds.
* setId: The isPermaLink attribute can be set (RSS2 only).

Since this project requires PHP >= 5.3 anyway, the check for this version is not needed anymore in Item.php.

It's now possible to specify an email address and an URI.

This was previously already possible by using the custom addElement function.

Add setContent() for Atom feed items

- Make it easy to get a <content> element on Atom entries
- Also spells "enclosure" correctly - "setEncloser" -> "setEnclosure"
- Fixes Atom test file on case-sensitive filesystems
- Tack a date_default_timezone_set() on tests, to avoid warnings

The namespace prefix and name can be set by invoking the addNamespace method of the Feed class.

See http://validator.w3.org/feed/docs/warning/MissingAtomSelfLink.html

It's actually the MIME type which is returned and then used for the HTTP Content-Type header field.

namespace FeedWriter

A minimal set of changes to support PSR-0-style autoloading:

- rename base class to \FeedWriter\Feed and FeedItem to \FeedWriter\Item
- break types out into \FeedWriter\ATOM, \FeedWriter\RSS1, and
  \FeedWriter\RSS2
- use class constants for versions
- make generateFeed() return a string rather than doing any IO itself
- add printFeed() to do output, if needed

My rationale for the last 2 items on that list is that our web framework
expects me to pass around strings, not do direct IO. I imagine needing
to grab the output and stash it in a variable or what-have-you is
a common use case, and it felt silly to have to wrap this in an
output buffer to accomplish that.

ATOM feed <author> element fix
Thanks for the fix!