Support more than parameter attributes attributes

[TimWolla]

since #3402 / php/phd#127 parameter attributes are supported, but other types of attributes are not yet.

Support should be added for all types of attribute. Class attributes are already in use (the #[\Attribute] attribute) and function / method attributes might be added with php/php-src#11293.

[haszi]

@Girgias Would the below markup work for class and function/method attributes?

<ooclass>
  <modifier role="attribute">AttributeName</modifier>
  <classname>DateTime</classname>
</ooclass>

<methodsynopsis>
  <modifier role="attribute">AttributeName</modifier><modifier>public</modifier> <type>string</type><methodname>CURLFile::getFilename</methodname>
  <void/>
</methodsynopsis>

[Girgias]

I think the proposed markup makes sense, and is compliant with DocBook 5.2

[haszi]

The class attribute on the class synopsis and function/method attribute on the function/method pages could look like this:

[haszi]

How should the method listings on class synopsis pages be handled? Attributes on above the method signature or on the same line?

[Girgias]

I think for methods it probably should be above the method signature, @TimWolla @kocsismate what do you think?

[TimWolla]

I agree. Putting it above the method would match the common userland style guides and it would better scale with a larger number of attributes (e.g. both #[\Deprecated] and #[\Override]).

Please also add the leading backslash for copy-and-paste safety with regard to namespaces.

[kocsismate]

Yes, above please! :)