improved wagn command

- uses OptionParser for the arguments 
- adds help for `seed` and `rspec` command (important change for rspec: special wagn and standard rspec options have to be separated by a double dash; see help ;)
- 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)
- spec helper easier accessible for mod developers ( it's no longer necessary to change the .rspec configuration file. The developer deck generator creates a spec/spec_helper.rb that requires the wagn spec helper)