Mazepy

- Added content-field to Cell-class and
added methods: setContent() and getContent().
- Changed Cell.toString()-method.

- Added braid-method to Grid-class.
- Added possiblity to export/import maze to/from JSON.

- Initial version.
- Includes Grid, Cell and Distances classes.
- Implements algorithms: Aldous Broder, Binary Tree,
Hunt And Kill, Recursive Backtracker, Sidewinder
and Wilson.