housekeeping

[abgordon]

Update readme, changelog, delete some old dockerfiles, update makefile

Explanation of why we had Dockerfile-iptables:

Updated dockerfile to build iptables

Coreos 1745.7.0 has an issue where version incompatibilites in
iptables, or ipsets, _or something_ was causing ipset references
in the iptables-save output to read "unsupported revision" instead
of referencing the ipset rule.

This commit adds a Dockerfile that builds iptables from source
in a stage, and installs it into the resulting ravel container.

For whatever reason, with iptables 1.8.x, we get cross-compatibility
between versions of coreos.

Dockerfile-alpine looked like cruft from a previous dev; not sure why they preferred it over the default Dockerfile.