This is the first part for #521: adoption of PHPStan's PhpDocParser.
For 5.0 I do not plan to introduce any more parsing features, but this should at least provide some validation consistency.

New behavior:

• [new] When the type is not simple enough -> exception
• [new] Understands (parser as a simple array) array shapes
• [new] Understands (parses as a simple object) object shapes
• Supports union & intersection types
• Parser all previously supported types
• Prases nullability in both forms (?, |null)
• Removes support for scalar type (BC break!)