Cleanup dependencies, remove ZEO leftovers

- remove now useless `zdaemon` dependency
- remove ZEO documentation
- update dependency list in README

patch time.time in historical_connections to avoid windows failures; fix race condition in pool.availableGC

* patch time.time in historical_connections to avoid windows failures.

* Also use a mock version of datetime.datetime.utcnow.

We can't patch the method in-place because it's an extension type.

* synchronize sleep with time

* increment by less than the pool timeout to avoid a race condition.

* Avoid mutating the dict as we iter over it.

Seen in Python 3.4 tests:

File "/home/travis/build/zopefoundation/ZODB/src/ZODB/historical_connections.txt", line 263, in historical_connections.txt
Failed example:
    conn = db.open()
Exception raised:
    Traceback (most recent call last):
      File "/opt/python/3.4.2/lib/python3.4/doctest.py", line 1324, in __run
        compileflags, 1), test.globs)
      File "<doctest historical_connections.txt[0]>", line 1, in <module>
        conn = db.open()
      File "/home/travis/build/zopefoundation/ZODB/src/ZODB/DB.py", line 761, in open
        self.historical_pool.availableGC()
      File "/home/travis/build/zopefoundation/ZODB/src/ZODB/DB.py", line 277, in availableGC
        for key, pool in self.pools.items():
    RuntimeError: dictionary changed size during iteration

Do3cc fix for45 master

Nested connections try to clean up themselves multiple
times. This does not work

Drop support for Python 2.6 / 3.2.

3.2 is no longer supported by our packaging / CI tools.

2.6 is long out-of-support from Python devs.

Cleanup tox.ini and .travis.yml as mentioned in #42 (and Python 3.5)

- (Both) Remove repetition of deps. Only install tests_require deps
  explicitly. The previous comment in tox.ini about eggs in the
  working directory doesn't apply, per @mgedmin.
- Setup Travis to use the local wheel cache for faster install times.

See http://zestreleaser.readthedocs.org/en/latest/versions.html.

Make zodbpickle non-optional. 

(IIRC a bug in python-modernize causes duplicate future imports)

Use PEP-426 environment markers

Any attempts to use platform_python_implementation or
implementation_name result in an "Invalid environment marker" error.

Any attempts to use >= to compare python_version result in an "Invalid
environment marker" error.

Augh documentation for all of this is painfully suboptimal.

Should fix #36

log ConflictError details, fixes #29

Update issue #22

Incorporate feedback and make the tests run under Python3. Notably, the Grand Exception Unification in Python 3.3 means that IOError is a synonym for OSError in those versions, but not before; deal with this by catching both types and throwing OSError in the doctests (because that's how it prints). Fix #21. Fix #22.

Fix #21, FileStorage: when disk space runs out while packing, do not leave the ``.pack`` file around

fixed ResolveableWhenStateDoesNotChange, changed show_tryToResolveConflict_log_output to check both cases