No brackets around wave vectors in `little_group` and `space_group_irreps`
Created by: attila-i-szabo
Does what it says on the tin: write spacegroupbuilder.little_group(pi,0)
instead of little_group([pi,0])
, and the same for space_group_irreps
. I didn't change the calling sequence of the private methods, for that is more convenient for writing the implementation. Solves https://github.com/netket/netket/issues/898