Improved PHP Expression parsing

• Improved PHP-expression parsing

$columns(subArray=['some-sub-array' => 'some-value'])

will now correctly parse to

<?php $columns = ['subArray' => ['some-sub-array' => 'some-value']]; ?>

• null, false and true scalars are now correctly handled and converted to the PHP boolean/null equivalent
• Added the possibility to single-line-comment inside attribute-blocks

(It actually compiles to something more useful, check the PHTML output, but this is what it essentially is for)

div(
    data-abc='abc',
    //data-omitted='this is omitted for now',
    data-def='def'
)