Add hint on even/odd operator, moved exersise down one paragraph (thw-python)

This PR 

* provides a hint and example usage for the modular division operator, which is not especially familiar to our audiences
*  moves the "create three variables with the following types" exercise to follow the paragraph on type coercion on which it depends.  No changes to the cells, just the order.

These respond to what-is-the-%-operator and you-didn't-tell-us-how-to-do-that-yet student hangups.