Opt branch

@acroy, thanks for the nice work. I created a pull request, since this facilitates adding line comments to the code. Hence, see below for further comments of further potential comments.
Here you could write
```julia
F=Base.LinAlg.expm!(scale(tsgn*tau,slice(hm,1:m+2,1:m+2)))
```
where you trust on the scale function to create a copy.