Fix tutorial and issue #209

[maynouf]

This PR fixes the documentation on the error reported in issue #209

A year ago I posted a fix for the error, but didn't submit any PRs (my bad).

I had the same issue that you had when trying to replicate the tutorial. Apparently the function set_wwr needs a construction parameter in the function, which by default is None. I replaced idf.set_wwr(0.6) with idf.set_wwr(0.6,construction="Project External Window"), which I believe is the default for windows defined in idf.set_default_constructions(), and now seems to be working correctly.

The branch from which I am submitting this PR (fix-tutorial) stems from the one called fix-collections, of which I submitted a PR some minutes ago, because without the fix to "collections" it is impossible for me to use the repo.