Packed Storage for symmetric, Hermite, and triangular matrices

[termoshtt]

Related to #74

https://www.netlib.org/lapack/lug/node123.html

Tridiagonal matrix support has been done in #196, and other formats, i.e. packed and band storage formats should be supported. It should be in lax crate, and exposed into ndarray-linalg.

[termoshtt]

FYI: https://stackoverflow.com/questions/28445648/convert-symmetric-matrix-between-packed-and-full-storage