Major reorganisation of the docs.

cli/answertests_docs.php

doc/docslib.php

doc/en/AbInitio/Authoring_quick_start_1.md

doc/en/AbInitio/Authoring_quick_start_3.md

doc/en/AbInitio/Authoring_quick_start_8.md

doc/en/AbInitio/index.md

doc/en/About/The_philosophy_of_STACK.md

doc/en/About/index.md

doc/en/Authoring/AnswerTests/Answer_tests.md

doc/en/Authoring/AnswerTests/Calculus.md

doc/en/Authoring/AnswerTests/Equivalence.md

doc/en/Authoring/AnswerTests/Form.md

doc/en/Authoring/AnswerTests/Numerical.md

doc/en/Authoring/AnswerTests/Other.md

doc/en/Authoring/AnswerTests/Results/AlgEquiv.md

doc/en/Authoring/AnswerTests/Results/AlgEquivNouns.md

doc/en/Authoring/AnswerTests/Results/CasEqual.md

doc/en/Authoring/AnswerTests/Results/CompSquare.md

doc/en/Authoring/AnswerTests/Results/Diff.md

doc/en/Authoring/AnswerTests/Results/EqualComAss.md