Add Python 3.6 and coveralls

[jamadden]

Drop python 3.3.

Minor misc project gardening.

Fixes #6

[tseaver]

In "days of yore", we avoided adding deps in the "bottom-most" ZTK packages (zope.event, zope.interface, zope.component, etc.) to stuff like zope.testrunner / zope.testing because they did indeed depend on one or more of them. If they no longer do so, then this should be fine.

[jamadden]

That completely makes sense to me! Circular dependencies are a special kind of torment, even in teat code. I worked hard to remove them recently in a lot of zope.app and other packages. I did a cursory check for the packages involved here and didn’t find anything (nothing low level depends on zope.event). I can look into presenting a more precise dependency graph.

[jamadden]

Here's what pipdeptree says:

zope.event==4.2.1.dev0
  - setuptools [required: Any, installed: 36.0.1]
zope.testing==4.6.2
  - setuptools [required: Any, installed: 36.0.1]
zope.testrunner==4.7.0
  - setuptools [required: Any, installed: 36.0.1]
  - six [required: Any, installed: 1.10.0]
  - zope.exceptions [required: Any, installed: 4.1.0]
    - setuptools [required: Any, installed: 36.0.1]
    - zope.interface [required: Any, installed: 4.4.2]
      - setuptools [required: Any, installed: 36.0.1]
  - zope.interface [required: Any, installed: 4.4.2]
    - setuptools [required: Any, installed: 36.0.1]

So it looks like we're clear.

[mgedmin]

LGTM

[jamadden]

Thank you!