Merge @aantonello commits.

This commit merges parts of:

https://github.com/aantonello/php.vim/commit/9d24eab4ea4b3752a54aebf14d3491b6d8edb6d8
https://github.com/aantonello/php.vim/commit/63c93d88253e5a93f46d04a3c363c61b12861b34

The syntax file is more closely aligned with the generic syntax highlighting
groups in Vim.

This didn't change highlighting for my custom syntax colours, hopefully it
will not affect others as well.
Merge @pixelastic commit.

This commit merges parts of:

https://github.com/pixelastic/php.vim/commit/8b4b165bab59fba80efda8dbe0e431605ab94669
Merge @joshtronic commit.

This commit merges parts of:

https://github.com/joshtronic/php.vim/commit/e9c5d0f6be019be3e5c37c3ef63994adeb4c125d

The 'finally' keyword was added to the list of recognised keywords.
Update template file and re-generate using PHP 5.5.7

$ php -v

PHP 5.5.7-1+sury.org~saucy+1 (cli) (built: Dec 12 2013 21:54:59)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
    with Zend OPcache v7.0.3-dev, Copyright (c) 1999-2013, by Zend Technologies
    with Xdebug v2.2.3, Copyright (c) 2002-2013, by Derick Rethans
Add 'yield' to the list of keywords (as of PHP 5.5).