Clean up FullPivHouseholderQR

Submitted by Benoit Jacob

Assigned to Benoit Jacob

Link to original bugzilla bug (#59)

Description

Make its API fully consistent with ColPivHouseholderQR. Make sure it doesn't do stupid things with thresholds.

It's OK to not have householderQ() and keep matrixQ() instead: having a householderQ() would be quite tricky. This decomposition is slow anyway.

Blocking

#48 (closed)