[eigen] Future for Eigen 2.0

[Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>]

Hello,

This message is prompted by a recent question on the forum about the 
LeastSquares module, which was in Eigen 2.0 but removed from 3.0.

People still find the Eigen 2.0 documentation (presumably via Google, but 
there is also a link on our wiki). Do we still need Eigen 2.0? Should we 
remove it from our website, or put a big notice that it is outdated?
For reference, Eigen 3.0.0 was released in March 2011, 3.0.1 in May 2011, 
and 3.1.0 in June 2012.

Following on, what about the Eigen2 compatibility mode in Eigen3? I doubt 
this is being tested properly. Are people still using it? Should we 
deprecate it in 3.2.1 (which we will probably release fairly soon?) with a 
view of removing it in 3.3?

All the best,
Jitse