Optional Build Number

Hi, I have added the possibility to specify the build number as maven property "build.number". This is good when you want to inject it from a CI software like Jenkins, TeamCity, etc.

I have also added a default value for skippedFails and undefinedFails parameters.

Please review. I'd love to have this change very soon in a stable release!

Thanks

P.S.: added some files to ignore in .gitignore, as well