hello-world: update tutorial to account for emptyStringIsComparedByValue()

[jtigger]

hello-world contains a blow-by-blow tutorial. We recently added a test case to help catch folks using the equals operator to detect an empty string (i.e. #280).

The tutorial needs an adjustment:

• the section titles assume there are three test cases; there are now four.
• this (new) second test needs some crisp explanation about the difference between comparing by value vs. comparing the reference without invoking too many concepts.
• the tutorial avoids the pitfall of using == for string comparison, let's keep that; this is about clarifying why this test matters.
• the audience of the tutorial are Early Programmers — people who are relatively newish to programming, but this is not their very first attempt at writing code.

[stkent]

FYI in light of exercism/problem-specifications#520 we may want to hold off on this change.

[jtigger]

doh!!!! :) Man, there goes many hours of effort into the rubbish bin. :-}

[jtigger]

Okay... the tutorial, as is, will serve as inspiration as we flesh-out the early part of the track.

• hello-world is/will be greatly simplified.
• looking at the current difficulty graph, we probably need to smooth that ramp out with some well-known early exercises.
• this tutorial could then be spread out across those exercises.

In light of that, this issue is no longer valid.