Merge api branch with api branch.

Readme.md

db/install.xml

db/upgrade.php

deploy.php

doc/en/About/Credits.md

doc/en/Authoring/Authoring_quick_start.md

doc/en/Authoring/Authoring_quick_start_2.md

doc/en/Authoring/Authoring_quick_start_3.md

doc/en/Authoring/CASText.md

doc/en/Authoring/Deploying.md

doc/en/Authoring/ImportExport.md

doc/en/Authoring/MCQ.md

doc/en/Authoring/Options.md

doc/en/Authoring/Question_blocks.md

doc/en/Authoring/Question_note.md

doc/en/Authoring/Sample_questions.md

doc/en/Authoring/Testing.md

doc/en/CAS/Equations.md

doc/en/CAS/Equivalence_reasoning.md

doc/en/CAS/Matrix.md