fdacluster 0.4.2

• Updated C++ code to use std::isfinite() on scalar values instead of
  arma::is_finite() which is meant for Armadillo objects. Also, replaced
  use of arma::is_finite() in favour of .is_finite() method of Armadillo
  objects.
• Better handling of precomputed data in vignettes.
• Skip examples and vignettes to accommodate some weird issues on some
  Rhub platforms.
• Fixes #17 which reported integer overflow when computing linear indices
  for large datasets by computing on the fly indices (i,j) from linear
  indices.