improved wagn command

- uses OptionParser for the arguments 
- adds help for `seed` and `rspec` command
- includes bugfix for chunk problems (http://wagn.org/Adding_a_script_to_the_head_tag)
- replaces irb with pry
- better TextMate integration for rspec (see http://xithan.clarify-it.com/d/cjl2cm)