Add support for timer, interrupt, and additional raw statistics

I needed access to raw stats like `vm:unix:*:vminfo:*` and `misc:cpu_stat:*:*:*` for a project I'm working on.  After some trial and error I ended up using the lookup tables from the [C version of the kstat command line utility from illumos-gate](https://github.com/illumos/illumos-gate/tree/861bfc8941f2c557f1bcb7a6d7f62f9da98ee4db/usr/src/cmd/stat/kstat) as well as parts of the selector code (so glob and regular expression matching is possible on each column).

I also added a few simple tests just as a sanity check.  I wanted to share my changes with you instead of trying to have two separate projects.

The syntax for using `ekstat:read/1,2,3,4,5,6` should be the same as your version, so projects [project-fifo/chunter](https://github.com/project-fifo/chunter) should be able to make use of the changes without any problems.

Check out the [CHANGES.md](https://github.com/potatosalad/ekstat/blob/0.2.0/CHANGES.md) for more information on features added in this pull request.