Run clang-tidy 7.0 with `-checks='-*,modernize-use-using' -fix`
against TU-s of all tests.
Manually refactor numerous typedef-s
- where missed by modernize-use-using check, not uncommon
- in code snippets in comments
Outcome is that searching for lower-case whole word typedef
in sources of all the tests should return no matches.
Add point2<T> alias template for backward compatibility with Boost <=1.68.
Replace multiple point_t aliases of point<ptrdiff_t> with single defined
in point.hpp. The point_t is common used to represent dimensions.
Replace many uses of point<ptrdiff_t> with point_t.
Apply reformatting around point2 changes to respect the line length limit.
Follows up discussion in #154
