start rebuilding the documentation

doc/sphinx/nbackend/expressions.rst

doc/sphinx/nbackend/type_system.rst

docs/.gitignore

docs/Makefile

docs/make.bat

docs/source/_static/img/logo.png

docs/source/api/index.rst

docs/source/api/kernelcreation/index.rst

docs/source/api/sympyextensions/astnodes.rst

docs/source/api/sympyextensions/field.rst

docs/source/api/sympyextensions/index.rst

docs/source/api/types/basic_types.rst

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docs/source/api/types/quick.rst

docs/source/backend/arrays.rst

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docs/source/backend/index.rst

docs/source/backend/jit.rst

docs/source/backend/kernelcreation.rst

docs/source/backend/rationale.rst