Added GetRandomSaltHexString method

First of all, great library!

I added a method for generating a random hex string based on generating a random salt. I've found myself doing this on a few occasions so I figured others might find this useful. 

I also added a .gitignore as well as a .gitattributes which allows for some of the ancillary files (like .suo or resharper files) to stop being tracked for commits. I then removed some of those files from the tracking cache. If you don't want those commits to be included, feel free to deny this pull request and I'll create a different pull request with just the new method (if that's okay).