…typos

* much more modular code
* jUnit testing introduction
  there are tests that run and do something,
  but they do not yet actually check something useful,
  except for exceptions
* test example images are now read as resources,
  so it should work more reliably

* more modularity
* less internal reliance on AWT
* less memory usage (more CPU)

... for possible future modularization

We use the Java method, because it allows us to keep the files for inspection if we want to.

Temporary files options:
* Java: files are deleted on JVM exit (or optionally not deleted at all)
* JUnit: files are deleted at end of test

* TiledImageMatrix
** now extends ImageMatrix
** uses dimensions instead of x&y / w&h
* AsciiExporter
** init(source) -> init(targetDimensions)