Ger: adding documentation stubs in apidocs

[lucbv]

Really not much to say beyond the fact that we forgot to do it while adding the ger function...

[eeprude]

I did not know about this, Luc. Thanks for adding it. I will add documentation for the next syr() and syr2() BLAS2 routines.

[lucbv]

No worries, I was not too aware of the documentation procedure until recently myself!
Let us wait for @e10harvey to look at this and if he likes it we can just merge, this should be a fairly lightweight procedure : )

[e10harvey]

Thank you!