add comments to deviantart engine
little refactoring
rewrite duckduckgo engine and add comments
add comments to dummy engine
update generalfile engine and add comments
update github engine and add comments
update piratebay engine and add comments
update soundcloud and add comments
add little comment
fix stackoverflow and add comments
fix startpage engine and add comments

* add language support
* remove not required code
* improve google-ad detection (no false detection anymore, I hope)
* other improvements
fix twitter engine and add comments

* add language-support
* add comments
* little refactoring
remove categories : social media from twitter engine in settings.yml
add little note to duckduckgo engine
fix wikipedia engine and add comments

* add paging support
* make number_of_results changable
* make result calculation more clear
* add comments
fix youtube engine and add comments

* add language-support
* decrease search-results/site to 5
* add comments
Merge pull request #89 from pointhi/engines

update search engines and add comments to it