v0.2.1- small bug fixes

• fixed a bug in index_builder which prevented the building of self defined indices
• fixed a still existing bug in transitive_reduction()
• added type = weights in indirect_relations()
• type = "identity" in indirect_relations() is now deprecated. Use type = "adjacency" instead.
• type = "weight" added to indirect_relations() to return the weighted adjacency matrix
  vertex names are now properly added as column and rownames to matrices produced by indirect_relations() and exact_rank_prob().