fix compile error when building w/o eigen3
PCA eigen-ized
SVD based PCA added
code cleaned
failing LMNN unit-test : test_pca_init changed
brief documentation updated + apply_to_feature_vector updated
PCA code cleanup
updating revision of data submodule
update data submodule : lmnn_modular changed
HAVE_LAPACK to HAVE_EIGEN3 and header changes