v0.0.0.9003

New features

• New parameter ret_nn: when TRUE returns nearest neighbor matrices
  as a nn list: indices in item idx and distances in item dist. Embedded
  coordinates are in embedding. Both ret_nn and ret_model can be TRUE,
  and should not cause any compatibility issues with supervised embeddings.
• nn_method can now take precomputed nearest neighbor data. Must be a list of
  two matrices: idx, containing integer indexes, and dist containing
  distances. By no coincidence, this is the format return by ret_nn.

Bug fixes and minor improvements

• Embedding to n_components = 1 was broken (#6)
• User-supplied matrices to init parameter were being modified, in defiance of basic R pass-by-copy semantics.