Errors found in `control_flow`

[despadam]

• in then conditionals quiz we use syntax print(1, end=",") but end was never explained
• 1st warm-up fix docstring to explain we expect (char, index)
• 2nd warmup: rephrase the expected result: "A list of integers containing all numbers from start to end (inclusive), in the correct order". Make it clear "correct order" means "canonical" or "natural" (the order of integers, either increasing or decreasing)