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
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