Preparing for a release.
Added utility for easily checking vobject equivalence.
Support for converting ANNIVERSARY

vcard 3 -> 4
------------

Find all X-ABDATE and X-ANNIVERSARY properties, and merge the ones with identical values. Convert all of these to ANNIVERSARY.

vcard 4 -> 3
------------

Convert ANNIVERSARY to both X-ABDATE and X-ANNIVERSARY.
PHP 5.3
Missing space.
select() all group properties without specifying the name
Support for multiple anniversaries in a vCard
remove unneeded whitespace
Simpler way to check UTF-8.

It avoids to call the `mb_check_encoding` function.
Merge pull request #156 from Hywan/string_utils

Simpler way to check UTF-8
Merge pull request #154 from fruux/anniversary

Support for converting ANNIVERSARY
Updated changelog and bumped version.
Merge branch '3.3' of github.com:fruux/sabre-vobject into 3.3
Merge branch '3.3'

Conflicts:
	ChangeLog.md
	lib/VCardConverter.php