Integrated optional junit xml output

Addresses #87, follows the 7 steps laid out in that ticket.

Adds 3 new configurations to CLI and guard config:
* junit - set to true to save output to xml files (false by default)
* junit_consolidate - rolls nested describes up into their parent describe blocks (true by default)
* junit_save_path - optional path to save the xml files to

Uses the junit reporter created by larrymyers from github/com/larrymyers/jasmine-reporters

Sample usage:

```ruby
guard :jasmine, :junit => true, :junit_save_path => 'reports' do
  watch(%r{^spec/javascripts/.+$}) { 'spec/javascripts' }
  watch(%r{^spec/javascripts/fixtures/.+$}) { 'spec/javascripts' }
  watch(%r{^app/assets/javascripts/(.+?)\.(js\.coffee|js|coffee)(?:\.\w+)*$}) { 'spec/javascripts' }
end
```

We needed to do this to get Jasmine results properly integrated in our Jenkins CI server, which is now working like a charm :)