Update test generator documentation.

[Insti]

Update the readme to better reflect the current best practices for test
generators.

[hilary]

I would also suggest using a consistent name for the name method (say that 3 times fast!)

The sample lib/$PROBLEM_cases.rb uses test_name, as does the list below it, but the sample example.tt erb reads <%= test_case.name %>. Doh!

A quick scan of the existing generators shows that the consensus name is name. 😄

[Insti]

Hmm name might be the wrong thing to use due to potential conflicts with the json file.
I'll have to check.

name is definitely the right name.

Reasoning:

• Desired usage in the erb (template) def <%= test_case.name %>
• We should not need to care at this level what is in the canonical data json file
• If the json causes a conflict this is a bug in ProblemCase creation code that needs to be fixed. (This bug does exist, but has not caused an issue ... yet.)

[Insti]

Addresses some of the issues discussed in: #485