Merge branch 'master' of https://github.com/ocelot-inc/tarantool into 1.6

doc/sphinx/book/administration.rst

doc/sphinx/book/app/a_errcodes.rst

doc/sphinx/book/app/b_internals.rst

doc/sphinx/book/app/c_lua_tutorial.rst

doc/sphinx/book/app/d_plugins.rst

doc/sphinx/book/app/e_sophia/i1.png

doc/sphinx/book/app/e_sophia/i10.png

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doc/sphinx/book/app/e_sophia/index.rst

doc/sphinx/book/box/admin.rst