Specifying Feed::createNewItem return data type for IDE completion

(cherry picked from commit d4913ed)

Replace invalid xml utf-8 chars in tag contents.

Feed::utf8_for_xml() method used in the Feed::makeNode() method.

This also makes pagination work with RSS1 feeds. The method parameter for the feed URL itself was removed, because RFC 5005 only specifies the other four link relations. The URL to the feed can be set with the setSelfLink method.

Added optional setPagination method that gives the possibility to add pagination links to feed pages

Added 'addCDATAEncoding' method

- 'addCDATAEncoding' accepts array of properties that are added to
'\Feed->CDATAEncoding' array
- provides more flexibility for folks that need finer control over the
way property values are rendered

Few fixes and applying coding standards

RSS2 constant is defined under Feed class

classes that are not part of the class namespace should have qualified names

Add the ability to choose the 'encoding' attribute

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.