ODESystem does not accept matrix variables

[baggepinnen]

I had to call vec below for the constructor to accept my parameter K, which is a matrix.

ODESystem(connections, t, ϕ, vec(K), systems=[armsys,motorsys])

It's not a huge problem, but the friction could be reduced by handling that automatically.

[ChrisRackauckas]

Yes, this one should have a good quick solution. Thanks for the issue. We should just vec internally.

[ChrisRackauckas]

I'm going to lump this into #605, which is all that array symbolics needs to change.