Matrix tests were not at the right place anymore

Especially, jdistlib could not be found but I had not noticed because
I had a lingering jar in core/src/test/java.
Documentation was badly phrased to the point of being incorrect
Fix out-of-date documentation
Small change to prepare for parallelisation

Indeed we will divide the horizontal B panel in blocks of columns.
Improved buffers for fast BLAS 3
Factor out panel-panel product

Thus create a matrix-matrix product based on a generic panel-panel
product (gepp). Less verbose variable names and implement index ranges as
lo..hi instead of lo..lo+l

Eventually our goal is then to provide a parallel version of gepp.
Prepare for testing of parallel matrix-matrix product
Fix typo in test printout
Parallel panel-panel product