Add iteratorsize

[oxinabox]

This should fix it with v0.5 of Julia. Re: all iterators are broken.
To be honest I haven't tested this version directly, am doing a quick commit and am relying on TravisCI to test it. If this doesn't CI I'll do a more careful branch and fix.

This problem is referenced in #46 (comment)

See: JuliaLang/julia#15977 and the linked documentation gist

[oxinabox]

Looks like this worked.
Failure currently showing is a timeout on one of the appveyer builds.
(I'm going to close and reopen to trigger another build)

[tkelman]

spaces around the =

[tkelman]

Thanks!

[oxinabox]

Cool.
This is my first code to have merged into someone else project.
Even if it is like 5 lines.
Yay.

[tkelman]

Good to hear - I could've sworn you had a base PR merged by now. If this thing with iteratorsize comes up often in other packages it would probably be worth putting it in Compat.jl.

[mschauer]

There is something I don't get here: what is the point of defining a fallback iteratorsize(v) for version < v"0.5.0-dev+3305" which gives an error but is less specific than the actual iteratorsize methods coming later?

[oxinabox]

@mschauer Good point.

I copied it direct from Iterators.jl
In particular from this PR

When I was doing so, it was on the logic that if iteratorsize was called in v0.4, it would not hit the Xml*Iter's iteratorsize-- which would result in undefined SizeUnknown. but would hit the generic one.

However that does not follow, because multiple dispatch is most specific first.

So it could just be:

if VERSION >= v"0.5.0-dev+3305"
    import Base: iteratorsize, SizeUnknown
end