edits to standardize the format of exercises

[eldobbins]

This PR is to address issues described in #461, which describes an exercise whose formatting could be improved. While working on that exercise, I found a couple more with formatting oddities, so fixed them too.

• Order of Operations
  • added numbering to match questions with solutions
  • reordered the questions so that the function parse_dates() is introduced before it is asked about
  • added a 3rd question about the None returned by parse_dates()
• removed the Python block formatting from Calling by Name because I think that section is part of the questions not part of the code
• added spaces to the items list in Encapsulating Data Analysis so the Markdown is parsed correctly
• Encapsulate of If/Print Block
  • fixed typo in the title
  • added and removed spaces from code examples to be more PEP8

I'm not satisfied with the wording of that last exercise. It asks 2 questions and then solves them before asking 2 more whose answers are in the Solutions block. I see that the exercise author is trying to chain concepts, but I'm not 100% sure it's successful. Please let me know if you want me to reformulate that exercise as part of this PR

[alee]

Reformulation of the exercise would be welcome, but we can have a separate PR for that - thanks again!

[eldobbins]

Maybe we could close the original issue #461 ?

[eldobbins]

I just checked the formatted rendering of the changes I made, and it's all screwed up. I'm going to try and fix that. I still have the branch. Can this PR be reopened or should I start a new one?

[eldobbins]

OK. I've fixed the formatting problems. The fixes are in the original branch. Please let me know how I should submit it.

[eldobbins]

Issued a new PR to fix this rendering problem.