- Added class NMFClustering for performing data clustering using iterative
  nonnegative matrix factorization (NMF). 
- Added class NMFConsensusMatrix for computing a consensus matrix from among
  multiple NMF clusterings. 
- Added classes ConnectivityMatrix and OrderedConnectivityMatrix for
  representing connectivity matrices.
- Changed abbreviation for nonnegative matrix factorization from NNMF to NMF in
  all class and method names.   
- Added single precision support for principle component analysis. Renamed class
  PrincipleComponentAnalysis to DoublePCA, and added FloatPCA.  
- Fixed bug in LinearRegression where default IRegressionCalculation was not
  thread-safe.
- Prevented duplicate column name in DataFrame. Duplicate names are now
  automatically suffixed with "_1", "_2",...,"_n".
- Added new overloads for StatsFunction.CovarianceMatrix() for FloatMatrix and
  StatsFunction.Covariance() for FloatVector.
- Added custom visualizer for DataFrame.
- Organized classes into solution folders inside Visual Studio.
- Added VS 2008 solutions for all examples and source editions.
- Added Add(System.Object) method to all types which implement IEnumerable.