Add better heredoc formatting and highlighting support

This code comes from Philippe Ivaldi’s pi-php-mode, with his
permission.  The only modifications to the code are small formatting
changes and moving much of the top to the top-level instead of within
the scope of define-derived-mode.

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
Add a test case for Github issue 38, related to heredoc support
Add Philippe Ivaldi to the contributors list for his heredoc code
Removed "then" as a PHP keyword.

There is no reference in the PHP docs as to "then" being a keyword or
reserved word.  This was causing font-locking problems with the Then()
function from Behat.

Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
Add Michael Dwyer to the list of contributors
Update php-mode-modified for the recent ‘then’ keyword patch
Merge branch 'better-heredoc-support'

* better-heredoc-support:
  Add Philippe Ivaldi to the contributors list for his heredoc code
  Add a test case for Github issue 38, related to heredoc support
  Add better heredoc formatting and highlighting support

Conflicts:
	README.md
Update php-mode-modified for the better heredoc support
Describe the improved heredoc support in the README
Revert "Merge branch 'better-heredoc-support'"

This reverts commit 94bc53ee81c6e795360aa19511f4d16b922a840d, reversing
changes made to 846c71d36bc82f2829fde0ed6bbd9780ef765dd0.

I made an error when incorporating the heredoc-related code from
pi-php-mode that causes most syntax highlighting to break.  This
reverts all of that code until I do a better job of debugging the
cause of the problem.

Github-issue: 56
Update php-mode-modified after reverting the heredoc changes