Release Name: 2.0.0

Notes:
This release fixes major bugs, adds support for Mentor Modelsim, and removes the $ruby_task callback.


Changes:
    *  The "cross-thread violation on rb_gc()" error has been fixed.
          o The "stack level too deep (SystemStackError?)" error has been fixed.
          o The 'test/unit' library can be used in Ruby test bench.
          o Mentor Modelsim verilog simulator works with Ruby-VPI. 

    * Removed $ruby_task callback and ability to dynamically register system tasks from Ruby because inter-process communication is complicated at present. 

    * Added piplelined ALU example. 

    * Tested and developed using Ruby 1.8.4 and Icarus Verilog 0.8, Synopsys VCS-MX X-2005.06-SP1, and Mentor ModelSim? 6.1d.