Speed up x14~: change "in_array" into "array_flip then isset"

Velocity of different ways: 
Array: 1.1413369178772
Regex: 0.32527613639832
ArrayKey: 0.082316875457764

```
<?php


function fromArray ( $word ) {
    static $_list = [
        // PHP keywords.
        '__halt_compiler', 'abstract', 'and', 'array',
        'as', 'break', 'callable', 'case',
        'catch', 'class', 'clone', 'const',
        'continue', 'declare', 'default', 'die',
        'do', 'echo', 'else', 'elseif',
        'empty', 'enddeclare', 'endfor', 'endforeach',
        'endif', 'endswitch', 'endwhile', 'eval',
        'exit', 'extends', 'final', 'for',
        'foreach', 'function', 'global', 'goto',
        'if', 'implements', 'include', 'include_once',
        'instanceof', 'insteadof', 'interface', 'isset',
        'list', 'namespace', 'new', 'or',
        'print', 'private', 'protected', 'public',
        'require', 'require_once', 'return', 'static',
        'switch', 'throw', 'trait', 'try',
        'unset', 'use', 'var', 'while',
        'xor', 'yield',
        // Compile-time constants.
        '__class__', '__dir__', '__file__', '__function__',
        '__line__', '__method__', '__namespace__', '__trait__',
    ];

    return in_array(strtolower($word), $_list);
}


function fromArrayKey ( $word ) {
    static $_list = [
        // PHP keywords.
        '__halt_compiler'=>1, 'abstract'=>1, 'and'=>1, 'array'=>1,
        'as'=>1, 'break'=>1, 'callable'=>1, 'case'=>1,
        'catch'=>1, 'class'=>1, 'clone'=>1, 'const'=>1,
        'continue'=>1, 'declare'=>1, 'default'=>1, 'die'=>1,
        'do'=>1, 'echo'=>1, 'else'=>1, 'elseif'=>1,
        'empty'=>1, 'enddeclare'=>1, 'endfor'=>1, 'endforeach'=>1,
        'endif'=>1, 'endswitch'=>1, 'endwhile'=>1, 'eval'=>1,
        'exit'=>1, 'extends'=>1, 'final'=>1, 'for'=>1,
        'foreach'=>1, 'function'=>1, 'global'=>1, 'goto'=>1,
        'if'=>1, 'implements'=>1, 'include'=>1, 'include_once'=>1,
        'instanceof'=>1, 'insteadof'=>1, 'interface'=>1, 'isset'=>1,
        'list'=>1, 'namespace'=>1, 'new'=>1, 'or'=>1,
        'print'=>1, 'private'=>1, 'protected'=>1, 'public'=>1,
        'require'=>1, 'require_once'=>1, 'return'=>1, 'static'=>1,
        'switch'=>1, 'throw'=>1, 'trait'=>1, 'try'=>1,
        'unset'=>1, 'use'=>1, 'var'=>1, 'while'=>1,
        'xor'=>1, 'yield'=>1,
        // Compile-time constants.
        '__class__'=>1, '__dir__'=>1, '__file__'=>1, '__function__'=>1,
        '__line__'=>1, '__method__'=>1, '__namespace__'=>1, '__trait__'=>1,
    ];
    return isset($_list[strtolower($word)]);
}


function fromRegex ( $word ) {
    static $_pattern = '(
        (a(bstract|nd|rray|s))|
        (c(a(llable|se|tch)|l(ass|one)|on(st|tinue)))|
        (d(e(clare|fault)|ie|o))|
        (e(cho|lse(if)?|mpty|nd(declare|for(each)?|if|switch|while)|val|x(it|tends)))|
        (f(inal|or(each)?|unction))|
        (g(lobal|oto))|
        (i(f|mplements|n(clude(_once)?|st(anceof|eadof)|terface)|sset))|
        (n(amespace|ew))|
        (p(r(i(nt|vate)|otected)|ublic))|
        (re(quire(_once)?|turn))|
        (s(tatic|witch))|
        (t(hrow|r(ait|y)))|
        (u(nset|se))|
        (__halt_compiler|break|list|(x)?or|var|while)
        )';
    return 1 === preg_match($_pattern, strtolower($word));
}


$keywords = [
    // PHP keywords.
    '__halt_compiler', 'abstract', 'and', 'array',
    'as', 'break', 'callable', 'case',
    'catch', 'class', 'clone', 'const',
    'continue', 'declare', 'default', 'die',
    'do', 'echo', 'else', 'elseif',
    'empty', 'enddeclare', 'endfor', 'endforeach',
    'endif', 'endswitch', 'endwhile', 'eval',
    'exit', 'extends', 'final', 'for',
    'foreach', 'function', 'global', 'goto',
    'if', 'implements', 'include', 'include_once',
    'instanceof', 'insteadof', 'interface', 'isset',
    'list', 'namespace', 'new', 'or',
    'print', 'private', 'protected', 'public',
    'require', 'require_once', 'return', 'static',
    'switch', 'throw', 'trait', 'try',
    'unset', 'use', 'var', 'while',
    'xor', 'yield',
    // Compile-time constants.
    '__class__', '__dir__', '__file__', '__function__',
    '__line__', '__method__', '__namespace__', '__trait__',
];


$counter = 0;
$times = [];

for ($i=0; $i<100; $i++) {
    $keywords[] = md5($i);
}


$times[] = microtime(true);
$loop = 1000;
while ($loop-->0) {
    foreach ($keywords as $keyword) {
        $counter+= fromArray($keyword);
    }
}

$times[] = microtime(true);
$loop = 1000;
while ($loop-->0) {
    foreach ($keywords as $keyword) {
        $counter+= fromRegex($keyword);
    }
}

$times[] = microtime(true);
$loop = 1000;
while ($loop-->0) {
    foreach ($keywords as $keyword) {
        $counter+= fromArrayKey($keyword);
    }
}

$times[] = microtime(true);
echo '$counter = ', $counter, PHP_EOL;

echo 'Array: '      , $times[1] - $times[0], PHP_EOL;
echo 'Regex: '      , $times[2] - $times[1], PHP_EOL;
echo 'ArrayKey: '   , $times[3] - $times[2], PHP_EOL;
```