2021 Refresh

Changes include:

• Documentation pass

• Iterator support (as-iterator.hpp - subscript_iterator_type)

• Type namespaces removed (now everything is in as::, functions accessed with mat_, vec_ etc...)

• More math functions (ceil, floor, round, snap, smootherstep, sign etc...)

• User-defined literal for real type (_r)

• No more point type

• Use C++ 17

• More constexpr

• Basis accessors for matrix types (generic row or column)

• Added screen_to_world and world_to_screen functions

• Improved Catch matcher for tests

• Enable many more warnings in test coverage

• Add cmake-format support

• Updated formatting (clang-format updates)

• More clang-tidy checks

• More template specializations

• Api renames (e.g. almost_equal -> real_near etc...)

• Updated compilers for Appveyor/Travis

• Lots more random improvements, fixes and updates...