AssertionError messages not parsed by IntelliJ

The current error messages as defined in the default templates are not is a form that IntelliJ parses for diffs:

```
Expecting someField of:

to be:

but was:

```

With a slight tweak IntelliJ does parse them and allows you to view the diff:

```
someField of expected: but was:
```

I believe Eclipse works the same way. Of course, this might be a bit less nice to read as plain text.

@joel-costigliola Is this something you have considered? Would you accept a pull request for this change?

Locate the default assertion-error message templates used by the generator and compare their current multiline format with the IntelliJ-compatible single-line example in the issue. Update the formatting so IntelliJ and Eclipse can parse diffs while preserving the reported field, expected value, and actual value; verify the generated messages in the relevant test coverage.

Written by the indexing model from the issue text.