Improved log levels and added logger injection, fixes #1

[aklinkert]

This PR basically does the following:

• [x] Add dependencies using go dep (Can be removed from the PR if you want to, there was just no dependency management so I added the (maybe soon to be default) godep one to install them
• [x] Added logger injection - logging.go now has two functions. NewDefaultLogger creates the package's default logger, NewLogger takes a logrus.Logger and returns the wrapped package Logger
• [x] Changed all log levels to specific log.Debug()/log.Error() instead of generic log.Print/log.Printf

I hope those changes are fine for ya. :)

Have a nice weekend and 👋🏻 from Hamburg, Germany! Alex

[jsimonetti]

I'm sorry I haven't been able to look at this yet. A quick glance does not show any problems and this should be merged. I hope I have some time this weekend to look at this and get it merged.

Thanks allready for the contribution!