added support for Atlassian's Bamboo

Hi, 
We've added support for Atlassian's Bamboo in the generated XML, and refactored the xml generator to use the go's template engine. Also added a parameter to select Bamboo as output. 
We were unable to test the xml with Jenkins as we don't have one running, but the generated xml is the same so it should work as before.
Regards.
Marcelo