Rebase the plugin on grok

[splitbrain]

This makes the plugin use Grok and codesearch.dokuwiki.org instead on relying on the no longer maintained phpxref.

I think it should work relatively well as a drop in replacement.

@Klap-in would be great if you could have a quick look before I merge this and bring it online.

related to #2 #3 and #4

[Klap-in]

I will try it later here some first notes.

[Klap-in]

In general it works. Of course, Gork works a bit different, so different usage choices are needed.

Not found:

  * A variable: [[xref>$USERINFO]] -- not found
  *  [[xref>DokuWiki_Auth_Plugin]] -- here the class name is use put in the path, for the new class names
      that is right. Of course this is then an exception.. 
  * [[xref>$_filename]] -- not found, unclear why not... because it is not defined..? 
      (maybe because $this->_fileName= is not recognized as definition by Grok?)
  * [[xref>$replacements]] -- is ok, definition is found. Wondering if 'Symbols' would be not more 
      useful for variables..

General point for discussion:
xref points to the definition (where the variable/function/etc is defined), not to the symbols (where it is used).
Is this desired?

• In a lot of cases I'm interested in how it is used, not in when it is defined..
• The previous xref interface listed both definition and usage, in two separate lists, on one page. But I do not see how to get this functionality back by using the Gork functionality.
• However, if a term is unique, it will directly open the code of the function/variable/etc. Clicking on the function, will do a symbol search (=usage search).
• [[codesearch>...]] does already a 'Full' search.

[Klap-in]

I'm a bit puzzeling, if there is an simple syntax to:

• request a 'symbol' search instead of 'definition' search.
• sometimes add a path to the search. (For example for 'meta' attribute in the renderer?)[[xref>meta@parser]] which changes in https://codesearch.dokuwiki.org/search?project=dokuwiki&full=&defs=&refs=meta&path=parser+OR+inc&hist=&type=&xrd=&nn=1&si=path&si=path (this uses refs instead of defs, just an example.) Does @ have a default use worth a xref? maybe in css..

[Klap-in]

I check this another time. I think it can work well.

Remaining case which I cannot explain is [[xref>$USERINFO]]. Therfore, no suggestions for improvement.

[[xref>$_filename]] was not working due to case-sensitivity, must be [[xref>$_fileName]].
[[xref>DokuWiki_Auth_Plugin]] is also not working, but that is because it is an alias. Therefore, it is logic OpenGrok is not recognizing it. That can be workaround with [[codesearch>DokuWiki_Auth_Plugin]].

I did a proposal for supporting arguments in the brackets of functions.

Further fine for me to merge and publish :-)