convert to ES6 classes and cleanup dependencies

[seriousme]

I converted the function objects to ES6 classes and cleaned up unused dependencies.
As "safe-buffer" is deprecated I have removed it as well.

As to benchmarks: results of local testing below

	Time in seconds
Node version	no-classes	using classes	Difference
6	7,2	7,46	3,61%
8	6,11	6,46	5,73%
10	4,69	4,88	4,05%
12	4,87	4,85	-0,41%
14	4,84	4,91	1,45%

Kind regards,
Hans

[mcollina]

lgtm