Port G(p, q, r) from GAlgebra.jl

[utensil]

See https://github.com/pygae/GAlgebra.jl/blob/master/src/ga.jl

Discussion on Slack:

Eric Wieser 21 minutes ago Perhaps as Ga.from_sig?

Eric Wieser 19 minutes ago Although I assume you also want a convenient shorthand

Eric Wieser 19 minutes ago Question is, should it behave like Ga.build and also return the basis vectors?

utensil 19 minutes ago OK, but I also want a API that resembles G(p, q, r) as we call it in daily life

Eric Wieser 19 minutes ago Clifford has ga, blade_dict = Cl(p, q, r), for comparison

Eric Wieser 18 minutes ago Which in my opinion was a mistake, we should have made it ga = Cl(p, q, r)

Eric Wieser 18 minutes ago I'm not opinionated on Cl vs G

utensil 18 minutes ago I'd like it to just return the ga as one would expect intuitively (edited)

Eric Wieser 17 minutes ago My worry is that G is a bit too short, unless you want users to use it as galgebra.G

utensil 17 minutes ago Cl is a constructor (edited)

Eric Wieser 17 minutes ago What do you mean by that?

utensil 16 minutes ago If we do the same thing, then it's Ga(p, q, r) ... (edited)

Eric Wieser 15 minutes ago Cl is not a constructor in clifford.

utensil 15 minutes ago Oh

Eric Wieser 14 minutes ago clifford.Layout is our galgebra.Ga, roughly

utensil 14 minutes ago Yeah, just check the code

Eric Wieser 13 minutes ago In theory, we could spell it Ga(sig=(p, q, r))

Eric Wieser 13 minutes ago We already have a sig argument to Ga, it just doesn't make any sense at the moment

Eric Wieser 12 minutes ago And we could make basis optional, inferring it as e_n from either g or sig

Eric Wieser 11 minutes ago But that's probably more work than adding Ga.from_sig(p, q, r), Ga.of_sig(p, q, r), or perhaps something wacky like Ga[p, q, r] (edited)

utensil 10 minutes ago I don't want to mess with the current constructor further (edited)

utensil 10 minutes ago it's already an overhead for callers