Drop support for Node.js < 4

[neocotic]

The current build contains unnecessary complexity as it tries to support Node.js 0.10 and 0.12 to some degree. I'd like to drop that support and simplify our build and contributor guidelines in the progress.

[neocotic]

To clarify; I do not intend on adding code the source code that would not run on 0.10 or 0.12 and, since we don't currently have unit tests, there is no safe guards that it ever does anyway. However, I'd like to remove support for these versions from the build so that it's much simpler and so that we can require npm@5 in order to take advantage of lock files etc.

[neocotic]

I will also be adding support for the newly released Node.js 8. This will only include running the CI build on node@8 for now.

This will obviously have more meaning if/when we get around to creating unit tests.