fix ZopeUndo.Prefix decode on python 2

Use python_requires and extras_require for version-specific deps

Fixes #93.
Fixes #92

Example:

```
$ pip install .
Processing /.../ZEO
ZEO requires Python '>=2.7.9,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*' but the running Python is 3.3.6`
```

runzeo clears socket files no matter what type of string address is

We need to use six.string_types in a few other places to account for the change in ZConfig. unix_domain_sockets() was failing before this on Python 2.

They now expire in the year 4755.

Fixes #90

Also remove an unused and duplicate import from that file and the
redundant `test_suite` declaration from the test file. There was also
a duplicate method definition in the test file that was removed.

Make all classes new-style. This is especially good for PyPy

See https://github.com/zopefoundation/ZODB/pull/160 for rationale.

Also restore PyPy to the build matrix.

- Better intro

- ReST improvements

- Spelling

- Less misleading WRT daemonization

- Removed dead log-configuration link

Fix (maybe) zeoctl and remove zeopasswd

Although it's hard to tell because IDK how to make earlier versions work.

Msgpack

AttributeError 'server' when StorageServer creation fails

Thanks!

Please travis!