bump version to v0.6-beta
updates RMQ library

* update RMQ_succint to RMQ_improved. This results in faster programs
  at slightly more memory consumption.
* fixes the memory leak by making the destructor of RMQ virtual.
* updates Makefile, configure.ac and Readme
* updates configure.ac and gitignore for non-posix archiver
removes incorrect check
canonicalize dsa_* function names
renames dsa_init -> dsa_new