SDSL 2.0.3

This version

• adds a K^2-treap implementation (k2_treap)
• fixes a bug in dac_vector
• adds rank_0/select_0 to sd_vector
• adds expand method for wavelet trees (WT algorithms)
• adds the sequence representation of Golynski, Munro and Rao (wt_gmr)
• includes a preliminary memory mapped version of int_vector (int_vector_mapper)
• cst_sct3 can now be parametrized to support fast navigational operations also on very large alphabets