Add php-mode-maybe and php-project-php-file-as-template

[zonuexe]

refs #362
closes #483

Spec of php-project-php-file-as-template

This variable is expected to be set by .dir-locals.el. You may set the value from the function added to php-mode-maybe-hook if it is difficult to set up the .dir-locals.el file in your project.

Set this variable to just t or nil or association list(alist).

If your project does not have an HTML template with a .php extension, just set nil. Conversely, if every .php file in your project is an HTML template, you should set t.

Suppose that your project has a mix of template .php files and script .php files. The settings are as follows if the template file has a specific directory or regular extension.

((nil (php-project-root . git)
      (php-project-php-file-as-template
       ("/tpl/" . t) ;; it means the file belongs to `tpl' directory
       ("\\.html\\.php\\'" . t) ;; it means the the file name has `.html.php' extension
       ("\\.php\\'" . nil) ;;it means that if this line is at the end of the list, then all other `.php' files are not template.
       )))

If you are not used to editing .dir-locals.el, be careful not to break the balance of ().
Read Per-Directory Local Variables of Emacs manual carefully for an explanation of the .dir-locals.el file.

An example of setting this variable to t or nil is as follows: (Don't forget .)

((nil (php-project-root . git)
      (php-project-php-file-as-template . t)))

Note: According to the Lisp specification, (A. (X Y Z)) and (A X Y Z) have exactly the same meaning.