Const Linear Algebra

Float-point code is from compiler_builtins via the constsoftfloat crate. Uses const generics to check shape of inputs. File an issue or PR a test if your use case is not supported.

```rust const START: SMatrix<2, 2> = SMatrix::new([[4.0, 1.0], [2.0, 3.0]]); const ADD: SMatrix<2, 2> = SMatrix::new([[0.0, 6.0], [0.0, 3.0]]); const EXPECTED: [[f64; 2]; 2] = [[0.6, -0.7], [-0.2, 0.4]];

const INVERSE: [[f64;2];2] = START.add(ADD).pinv(f64::EPSILON).finish(); for i in 0..2 { for j in 0..2 { assert!(float_equal(INVERSE[i][j], EXPECTED[i][j], 1e-5)); } } ```