Shields.io, Windows support, new setup.py, codecov

Started working on non-Redis broker support. Updated supporting files
like setup.py/travis/README to the same ones used in my other projects.
MD to RST, AppVeyor fix.

Converted README.md to reStructuredText, thanks to PyPI. No more
manually converting after sdist upload.

Fixing redis-server command error in AppVeyor.
Fixed appveyor again, no more eager tests.

Forgot to convert bash commands to batch commands in appveyor.yml.
Setting env variables properly.

Instead of using CELERY_ALWAYS_EAGER, I'm launching a real Celery
working in a thread under the same Python process.

Moved Celery and Flask app instances into a dedicated module. No longer
testing on different Flask/Celery instances, just one instance of each.
Fixed Windows env var values.

Found out that space between the value and the two ampersands was being
included in the variable. Works on my Win10 VM.
Testing with Redis and Socket files.

Doesn't work on my Windows10 VM but maybe it works on Travis with 2012?
Started refactoring for multi-broker support.

Gave up on Redis sockets on Windows.
API breaking changes.
Retry on backend URL.

Looks like Celery raises NotImplementedError on url properties.
Also forgot to remove statements from appveyor.yml in the previous
commit.
Fixed Redis socket exceptions.

Using another approach at determining the Celery backend.
Split _LockManagerRedis into that and _LockManager for future managers.
Reorganized code. Commit before refactoring more.

On a mission to make this even more testable.
Better testing of single_instance().

Thoroughly testing the decorator, unlike before. Made _LockManager and
its derivatives more testable.

Fixed some testing bugs too.
Testing include_args more thoroughly.
Started testing timeout.
Tested timeout.

Including Celery app config in deciding on timeout value.
Getting rid of pickle warning during testing.
Small fixes, improved testing.
Using Celery's Redis backend.

No longer using flask.current_app to get Flask-Redis-Helper's redis
handler for single_instance support on redis. Using Celery's backend
engine instead.
Got DB backend working.

Testing with SQLite only for now. Need to setup MySQL and PostgreSQL on
both CI environments.
Adding MySQL to CI environments.

PyPy seems to not work with sqlite. Dropping support.