Enable strict text checking by default

[niknetniko]

• Text is now checked strictly be default: there must be an exact match.
  • The option ignoreWhitespace is still present and can be used to revert to the current behaviour if needed.
• By default, we ensure that the expected values for stdout/stderr in the DSL end with a newline.
  • We only add a newline if there is none.
  • This can be disabled by setting normalizeTrailingNewlines to false.
  • We also apply this when using custom oracles.
• We don't do this for JSON test suites, so those should be updated (but apart from a few non-used exercises from us, no one uses the JSON test suites, so I don't think this is a problem).

Fixes #462.