Add a release tag

[kostyfisik]

Please, add a release tag for ease of referencing directly to the latex source, e.g. y2017 can be a good name for tag.

It can also be a good idea to attach a PDF file to the release - in the case of an outage of http://www.eecs.wsu.edu/~schneidj/ufdtd/ it can be a good option to download a book for those, who are not really good in LaTeX to make it from source.