Add matrix operations

[liebharc]

Add matrix support.

Next steps:

• Figure out what operations we need (e.g. addition, mulitplications, interpolation, convolution)
• Decide on what data structures are necessary (e.g. MxN matrix to store several vectors and MxNxO matrix which stores several impulse responses and can be convoluted with a MxN matrix)
• Decide which operations should be implemented in this lib because they operate on large amount of data. I would hope/expect that for most operations another Rust lib can be found so that we can keep the matrix implementation small.

[liebharc]

There is for sure more what could be done, but with ´0.4` we made a first attempt on this. So closing this issue.