- Fix trait observations in PHP >= 7.0

- Correctly label function as having variable arguments in the
  case where the function has some required and some default
  arguments.

Fix a couple of crashes when recursing the AST.

Don't use NULL source expressions in variable callbacks.

* Nullable types

* void functions
* Array destructuring
* Class constant visibility
* Multi-catch exception handling
* Support for keys in list()
* Negative string offsets

See http://php.net/manual/en/migration71.new-features.php

AnyExpressionObserver tweaks.

Fix compiler warning for missing enum value in a switch statement.

PHP 7.0 support

* Parameter type declarations
* Return type declarations
* Null coalesce operator
* Spaceship comparisons
* Anonymous classes
* Grouped imports
* Return generators
* Array constants with "define()"

See http://php.net/manual/en/migration70.new-features.php

Support for PHP 5.5 and PHP 5.6 source code.

Comment updates

Capture consecutive comments instead of dropping all but the last one. This
also helps with parsing variables from PHPDocs, as this code
snippet now detects 3 variables:

    /* @var $this \\yii\\web\\View */
    /* @var $name string */
    /* @var $message string */
    function myPublicStatic() {
        // ...
    }

A small release with the following fixes

1. Line number on property declarations was being reported incorrectly.
2. @var typehints are now being parsed from /** comments. They are
   also flagged with a new property VariableClass::IsPhpDocVariable