Stackoverflow in toExampleValue() for python client

[fbl100]

Added a Set in toExampleValueRecursive() to keep track of which models we have
generated to avoid an infinite recursion for recursive models. An example of a recursive
model would be a GeoJson GeometryCollection.

@spacether This is a retry of the prior PR that was reverted due to an OS line ending issue.

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[spacether]

Thanks for the new PR! What code did you change to fix the line end issue?
Because there is only one commit I can't tell. Is it:
expectedValue = expectedValue.replaceAll("\\r\\n", "\n");?

[fbl100]

@spacether Yes, that was it. Sorry, I try to rebase/squash on my side (habit at my day job).

[spacether]

Closing and re-opening to try to kick off travis

[spacether]

Thank you for your new PR with the fix!
Merging here and keeping an eye on CI tests...