tensors of low rank and low dimension

[lgarithm]

Provide tensors with low rank and fixed dimensions, for geometry and graphics. Especially,

shape	name alias	usages
(2)	2d-vector	planer coordinate, planar disposition
(3)	3d-vector	spatial coordinate, spatial disposition
(2, 2)	2-by-2 matrix	planer linear transformation
(3, 3)	3-by-3 matrix	planer affine transformation, spatial linear transformation
(4, 4)	4-by-4 matrix	spatial-affine transformation

what's more https://en.wikipedia.org/wiki/Generalized_coordinates

shape	name alias	usages
(2, n), (n, 2)		point in the configuration space of n planer free particles
(3, n), (n, 3)		point in the configuration space of n spatial free particles

[lgarithm]

Those tensors should be implemented as

using vec2d = basic_tensor<R, 2, std::integer_sequence<2>>;
using vec3d = basic_tensor<R, 2, std::integer_sequence<3>>;
using pos2d = basic_tensor<R, 2, std::integer_sequence<2>>;
using pos3d = basic_tensor<R, 2, std::integer_sequence<3>>;

using mat2d = basic_tensor<R, 3, std::integer_sequence<2, 2>>;
using mat3d = basic_tensor<R, 3, std::integer_sequence<3, 3>>;
using mat4d = basic_tensor<R, 3, std::integer_sequence<4, 4>>;

without over head.

And they should be able to replace https://github.com/lgarithm/drawings/tree/master/engine/src/rey/linear without losing performance.