added base class for AJD and an example of a derived class header
added JADiag.cpp and made some of the other suggested edits
fixed some minor mistakes so that it builds
swithed to cmath for machine eps and changed includes format
changed pointer V0 to use an emtpy SGMatrix
added a unit test for JADiag and ifdefs for eigen3
Merge pull request #1205 from pickle27/develop

added base class for AJD and an example of a derived class header