Add more fns

[Richard Cotton]

checks for diagonal, identity, positive-definite (see https://www.mathworks.com/matlabcentral/newsreader/view_thread/55350), unit, upper or lower triangular, orthogonal/unitary matrices.

[Richard Cotton]

Mostly fixed via https://bitbucket.org/richierocks/assertive.matrices/commits/e28dde0488536b85aee1bef8e8d3d8b8dfca571b https://bitbucket.org/richierocks/assertive.matrices/commits/a0dc855a4f94ed9f3c6fee9ff8844eeb06a6a70e

Still need to add fns for +ve definite matrices.