updated version from 2015 to 2018

[MathisWellmann]

using Rust version 2018 and fixed the resulting errors, no logical changes to the library just refactoring

[pengowen123]

Thanks for the contribution! I noticed a few small things, but overall this looks good 👍

[MathisWellmann]

Thanks for actively looking at my PR. I'm rather new to creating pull request to other repos and originally only intended to merge the first two commits but apparently once I added more commits to my own fork it shows up here as well. regardless I kind of like all the commits as it pretty much just extends the Activation enum to more functions and provides useful methods. With the last commit I resolved your suggestions and it should hopefully be ready to merge.