chore: semantic-release and circleci

[ForbesLindesay]

This will move packages to CircleCI. It also adds a "publish" job that will publish the package according to Semantic Release.

This will make it much easier to maintain the packages as there will be a single jstransformers account on npm that is responsible for publishing all packages, and all we will need to do is review/merge PRs as appropriate.

[ForbesLindesay]

I removed the HISTORY.md file as semantic-release automatically maintains release notes in the GitHub releases.

I also removed the "version" field from package.json because semantic-release automatically adds the appropriate version just before publishing, and doesn't keep the version in git up to date.

[RobLoach]

Good call... We'll have to remember to remove private from the packages that use this. 👍

[RobLoach]

Agree about the removal of HISTORY.md ... There isn't a real big need for it.

[webketje]

@ForbesLindesay @RobLoach Any chance to get this merged so the rest of the jstransformers can be updated?
Perhaps the test run fails on Node 8 because xo@0.25.4 is the latest compatible version (output from npm info xo@* engines.node) but package.json has a "xo": "*" dependency?

Perhaps it's an option to rename posttest and enforce the style before the CI runs? (eg with husky)