GSoD week 9

 Hi!

Week 9 has been quite productive and I'm happy with the results, even though I haven't met my target of completing doxygen review on all high priority files.

The remaining files from the common folder are done and in PR#2627. They have been reviewed by @criezy (as always, huge thanks for the swift review) and I'm hoping we will get that merged soon.

I have also finished my work on headers from the engines folder and they can now be found in PR#2633. Four of these files have been categorized as high priority and to the remaining ones I have added a doxygen group definition so that they appear in the right place in the structure.

The engines headers gave me a bit of a headache and I had to spend much more time on them than initially planned. First challenge was to grasp all the concepts of engine, meta engine, Advanced Detector and how they relate to one another. I also had to make sure the references to various methods and structures that are declared in other files are resolved properly. Without any exaggeration, I can tell you that when reviewing a 700-line long file, I probably rebuild it about 50 times as I crawl through it, to make sure everything looks correctly. Fun!

I am now working on five files from 'graphics', they will be in PR very soon. Then one file from 'image' and three files from 'audio' and the high priority ones will be finally done.

This post is coming late (as usual), the next one will be here soon.