Add semi-normal solvers

[MaxenceGollier]

#109
The next step would be to automatically call these functions in qrm_least_squares and qrm_min_norm when qrm_set(spfct, "qrm_keeph", 0) has been previously called.
I still have to figure out how to do it because spfct is not an argument of these functions.
Maybe add qrm_keeph :: String = 1 as a keyword argument ? Let me know what you think when you have some time !
@dpo, @amontoison

[amontoison]

I suggest to add a keyword argument seminormal::Bool=false in the functions qrm_least_squares and qrm_min_norm.

[MaxenceGollier]

Done in aa934fc.

[MaxenceGollier]

What do you think of this now ? @amontoison
I will open a PR for a Golub-Riley implementation once this has been merged @dpo.

[amontoison]

It's fine for me, Maxence.
Until I hear something from Dominique (such as an approval), I won’t merge the PR.
This way, it will avoid any overlap with what you are working on together.