Revision 1388099

MATH-863
New "Quaternion" class. Thanks to Julien Anxionnat.
After applying the original patch, the following changes were made:
* Renamed the "static" quaternion instances ("PLUS_" prefix removed).
* Removed some (syntactic sugar) methods; removed or modified corresponding
  unit tests.
* Made the redundant accessors call the "canonic" ones.
* Removed the default tolerance and added an explicit tolerance parameter
  in methods that depend on equality testing.
* When a "ZeroException" is thrown, the actual value of the norm is provided
  in the detailed message (as the implementation actually does not use a
  strict comparison with 0).
* Added "equals(Object)" and "hashCode" methods.
* Javadoc and formatting. Added license header.
* Removed "toString" documentation (as this representation should not be
  binding). Changed the representation to not use a comma.
* Renamed "scalarMultiply" to "multiply".
* More stringent tolerance used in the unit tests assertions, whenever
  possible.
* Added unit tests.