Implement `sum` for LogWeight

[dlfivefifty]

I'd like to be able to do the following:

x=Fun()
sum(log(abs(x-0.1)))

partly to check SingularIntegralEquation's logkernel.

[kburns]

Would this be easy to add? It would be great for simple BIEs.

[dlfivefifty]

You can use SingularIntegrals.jl? It's a slightly different paradigm but can compute such integrals very fast

[kburns]

How does that handle near singularities? Global refinement? QuadGK actually seems to be working pretty well for this particular case too.

[dlfivefifty]

it has an exact formula for log kernel of OPs. It's much much faster than QuadGK and the cost is uniform as you approach the interval

[dlfivefifty]

read my paper with @MikaelSlevinsky for info

[kburns]

Ok I'll take a look, thanks!