export all functions starting with gsw_

[Alexander-Barth]

Do we agree to export all functions names starting with gsw_ ? Instead of calling GibbsSeaWater.gsw_t_from_ct we would just call gsw_t_from_ct.

[ax1ine]

I think it's a good idea!

[Alexander-Barth]

There are also some function like this: (3 output arguments)

gsw_specvol_alpha_beta(sa::Float64, ct::Float64, p::Float64, specvol, alpha, beta)

In Julia, this would be more convenient:

specvol, alpha, beta = gsw_specvol_alpha_beta(sa::Float64, ct::Float64, p::Float64)

function gsw_specvol_alpha_beta(sa::Float64, ct::Float64, p::Float64)
    specvol = Ref{Float64}()
    alpha = Ref{Float64}()
    beta = Ref{Float64}()
    gsw_specvol_alpha_beta(sa,ct,p,specvol,alpha,beta)
    return specvol,alpha,beta
end

We could choose to export only the 3 input argument function.