Divide functions for the PHP manual to php.el and php-local-manual.el

[zonuexe]

I have split the functions that are not related to the processing as major mode into other files.

• Added manual https://github.com/emacs-php/php-mode/wiki/Local-PHP-Manual

New variable

php-search-documentation-function custom variable

Replaces function to search for the keyword at the cursor position.

• default: #'php-search-web-documentation

(custom-set-variables
 '(php-manual-path (expand-file-name "~/local/share/php-manual"))
 '(php-search-documentation-function #'php-local-manual-search))

BC break

No longer refer to the local manual unless you set php-search-documentation-function.