Martín Noblía

Add `expm` (exponential matrix) implementation

11

https://en.wikipedia.org/wiki/Matrix_exponential

we need more examples from `transformations.rs`

for some operations could be nice have a `Mnn` impl for all the basic operations and maybe also impl `LinearAlgebra` trait

We have a problem that don't allow calculate `inv()` method for types which are not floats(`i32`, `i64`, `usize`) because the trait impl is only for `Float`

Maybe we need a `cond(A)` method for the `expm()` implementation #4

This function is useful for a lot of applications, like simulations, robotics, ...etc...