Treat `const` as a keyword instead of a type-hint

PHP does not use `const` as a type-hint like it does with `array`,
`callable`, and so forth.  Semantically we should treat it as a
built-in keyword instead.
Add `enddeclare` to the list of keywords

This list at

    http://php.net/manual/en/reserved.keywords.php

shows that this is a reserved keyword in PHP.
Treat `eval` as a built-in keyword
Show links to the official site and wiki when customizing PHP Mode

This patch adds two URLs to the information for the PHP Mode group so
that when users run `M-x customize-group` they will see links to
websites with additional information about PHP Mode.
Update php-mode-modified for changes made today
Fix regex for namespaces in function calls

The regular expression we use to apply syntax highlighting to
namespaces in function calls breaks when it comes to sub-namespaces.
That means that PHP Mode highlights

    \Foo\bar();

correctly but it messes up

    \Foo\Bar\baz();

The proper font-face is only applied to the inner-most namespace, i.e
‘\Bar’ instead of the full ‘\Foo\Bar’.  This patch corrects that
problem so that the full namespace has the correct face.

GitHub-Issue: 26
Signed-off-by: Eric James Michael Ritz <lobbyjones@gmail.com>
Add FILTER_SANITIZE_FULL_SPECIAL_CHARS to the list of constants

See the list at

    http://us3.php.net/manual/en/filter.filters.sanitize.php

for information about the constant and its use.
Fix an error about php-extra-constants being void

It is possible for us to byte-compile PHP Mode and receive an error
about php-extra-constants being void as a variable.  We can correct
this by using the ‘autoload’ magic comment to make sure Emacs
evaluates the defcustom call that defines the variable.

GitHub-Issue: 120