Merge pull request #1190 from maths/proof-builder

corsscripts/sortable.css

corsscripts/sortable.min.css

corsscripts/sortablecore.min.js

corsscripts/stacksortable.js

corsscripts/stacksortable.min.js

doc/en/Authoring/Matching.md

doc/en/Authoring/Parsons.md

doc/en/Developer/Development_track.md

doc/en/Topics/Matching.md

doc/en/Topics/Parsons.md

lang/en/qtype_stack.php

stack/cas/castext2/blocks/parsons.block.php

stack/maxima/contrib/matchlib.mac

stack/maxima/contrib/prooflib.mac

tests/parsons_block_test.php

thirdpartylibs.xml